Abstract: The natural rubber (Hevea brasiliensis Muell. Arg.) industry is of great significance for the sustainable economic and ecological security in the tropic areas. It is very urgent to resolve the depletion of soil fertility in rubber plantations in recent years. Fertilization can be expected to directly enhance the soil quality and microenvironment. Nevertheless, the excessive application of chemical nitrogen fertilizers can also lead to nitrogen leaching and soil degradation. The chemical nitrogen and organic fertilizers can be combined to enhance soil nutrition, quality, and productivity. However, it is unclear on the effects of different fertilization modes on the soil quality in the rubber plantations. In this study, a 12-year field experiment was conducted on a rubber plantation in Hainan, China. Four treatments of fertilization were implemented: chemical fertilizer application alone (NPK, the total amount of fertilizer applied was 1.0 kg/tree chemical fertilizer (N:P₂O₅:K₂O=15:9:6)), a combination of 50% chemical N fertilizer and 50% co-composted organic N fertilizer application (NPKO), a combination of 50% chemical N fertilizer and 50% composted organic N fertilizer application (NPKM). The control (CK) was taken as the rubber plantation in the same area with no fertilizer application. All fertilization (chemical or organic fertilizer) treatments shared the same total rate of N application. Soil samples were collected from the 0-10 cm and 10-20 cm soil layers. A systematic analysis was made to evaluate the soil physicochemical properties, and enzyme activities, as well as the microbial carbon and nitrogen. Principal component analysis (PCA) was employed to construct the minimum dataset. A comprehensive evaluation of the soil quality was then performed on the various treatments of fertilization. The results indicated that significant differences were observed in the soil nutrient levels among the four treatments of fertilization. 1) The NPKO, NPKM, and NPK treatments significantly increased the soil pH, organic carbon, and total nitrogen contents in the 0-20 cm soil layer by 2.39%-12.92%, 17.72%-96.51%, and 32.28%-97.20%, respectively, compared with the CK. 2) The NPKO treatment significantly increased the total phosphorus, total potassium, and soil available nutrient content in the 0-20 cm soil layer. While none of the treatments significantly affected the carbon, nitrogen, and phosphorus stoichiometric ratios. 3) There was a significantly lower trend in the urease activity in the 0-10 cm soil layer and acid phosphatase, β-1,4-glucosidase, and β-1,4-N-acetamido-glucosidase activities in the 10-20 cm soil layer in the NPKM treatment than those in the CK. The remaining enzyme activities showed no significant change in all treatments. 4) All three fertilization treatments significantly increased the soil microbiomass carbon and nitrogen content. Among them, the NPKO and NPKM increased more than the NPK. 5) The evaluation index systems of TDS and MDS were used to calculate the soil quality indices of the rubber plantations under the different fertilization treatments. The scatter plot of the soil quality index was fitted to the total and minimum datasets. There was a significant positive correlation (R²=0.85, P<0.001). The MDS was expected to replace the TDS better than the cultivated horizon soil quality index. Nine indicators were selected for the MDS evaluation index system using PCA: SOC, TK, TP, ACP, NH₄⁺-N, CAT, NAG, C: N, and MBN. The soil quality index ranged from 0.31-0.78, averaging 0.52 at medium levels, with the descending order of the NPKO>NPKM>NPK>CK. The soil quality index after NPK shared no significant improvement, compared with the CK treatment. However, the soil quality after the NPKO and NPKM at the depths of 0-10 cm and >10-20 cm increased by 75.19%, 110.76%, 36.20%, and 16.34%, respectively (P<0.05). Consequently, the combined application of organic and chemical fertilizers effectively alleviated soil acidification for better nutrient status and fertility levels; The NPKO treatment was the second most pronounced enhancement in the soil nutrients and quality. Therefore, the combination of organic fertilizer and chemical fertilizer, particularly composted organic fertilizers, can be expected to serve as a viable fertilization strategy for the high soil fertility and quality in the rubber plantations of Hainan Island.