Abstract: To investigate the effects of fertilization on teak growth and understory vegetation diversity,the fouryear-old teak Tectona grandis L.f.plantation in Guangxi was studied by randomized block design and carried out different kinds of fertilizer treatment respectively（included F1:0.5 kg NPK complex fertilizer,1.0 kg calcium fertilizer and 1.0 kg MgSO₄ fertilizer;F2:1.0kg NPK complex fertilizer,0.5 kg calcium fertilizer and0.5 kg MgSO₄ fertilizer;F3:1.0 kg NPK complex fertilizer and 0.5 kg MgSO₄ fertilizer;F4:1.0 kg NPK complex fertilizer;CK:no fertilization）.The results showed that fertilization significantly accelerated growth of teak tree height,diameter at breast height and volume.Compared with control,the average annual increment of H,D_BH and V increased 0.13-0.32 m,0.17-0.26 cm and 4.35-9.63 dm~3,respectively.The growth increment of F3 was the largest,and the growth rate of D_BHand V promoted significantly by 10.35%and 10.55%than CK.Understory vegetation types of young teak plantation were relatively abundant and involved 25 families,39 genera and 42species,among which Compositae and Gramineae were the main dominant species.There were significant distinctions in Shannon-Wiener index（H′），Simpson index（D）and Pielou evenness index(J_sw)（P＜0.05）and these indexes of F1 and F3 treatments were significantly higher than CK,but the Gleason species richness index（D_g）was no significant（P＞0.05）between five treatments.The comprehensive evaluation scores of 12 indexes that included tree growth and understory were F3,F1,F4,F2,CK in turn.The rational fertilization of 4-year-old young teak plantation could promote the growth of trees and increase the richness and diversity of understory.The low-input application of 1.0 kg NPK fertilizer and 0.5 kg MgSO₄ fertilizer in young teak plantation is more beneficial to the growth and community stability.