Abstract: Understanding the characteristics and mechanisms of rural settlement morphological evolution provides a basis for scientifically regulating human–land relations in karst regions. However, under the combined pressures of rapid urbanization, rural population outflow, and ecological governance, the evolutionary patterns of settlement morphology in karst areas remain insufficiently documented. Taking Guangxi Zhuang Autonomous Region as the study area and drawing on long-term multi-source time-series data from 1990 to 2020, this study integrated exploratory spatial data analysis (ESDA), landscape pattern indices, the rank-size rule, and the geographical detector (Geodetector) model to reveal the evolutionary characteristics and driving mechanisms of rural settlement morphology in a typical karst region of Southwest China from the four dimensions of location, size, type, and expansion mode. The results show that: The overall pattern of rural settlement density in Guangxi, decreasing from the southeast to the northwest, remained relatively stable, while the center of gravity shifted from southeast to northeast and then to northwest. The settlement size distribution exhibited a rank-size distribution pattern, with Zipf indices below 1 for all periods; small settlements were widely distributed, while the proportion of large settlements increased steadily. The settlement size showed a relatively stable spatial pattern characterized by high values in southern Guangxi and low values in the northeast. Positive morphological evolution was dominated by the slow-growth type, whereas negative evolution shifted from the disappearance type to the shrinkage type. Small settlements experienced drastic disappearance, whereas large settlements remained relatively stable; the spatial pattern of settlement expansion and shrinkage shifted from concentration to dispersion. Expansion was dominated by the edge-expansion mode, while enclave-type disappearance maintained a high proportion over the long term, showing pronounced spatio-temporal differentiation between settlement expansion and disappearance. Natural factors such as elevation, slope, and cultivated-land resources imposed fundamental constraints on the morphological evolution of rural settlements: the q value of cultivated land for settlement size consistently ranked first among all detection factors, its q value for settlement density approached 0.35 (P<0.01), and the elevation–cultivated land interaction fluctuated around 0.90. Socio-economic factors constituted the endogenous driving forces through population change and economic development, with rural population showing q values above 0.60 (P<0.01) for settlement size and farmers' per-capita net income ranking first for settlement density; and policies and institutions, through resource allocation, gave the evolution distinct regional disparities and stage-specific characteristics. Specifically, relocation policies such as ecological migration and poverty-alleviation relocation may have contributed to the enclave-type disappearance of scattered settlements in eastern, southern, and western Guangxi; by the end of 2019, 710 000 people had been relocated in Guangxi under poverty-alleviation relocation programs. Meanwhile, comprehensive land consolidation and land-use regulation may have promoted the infilling expansion of settlements in the plains of central and southeastern Guangxi.The morphological evolution of rural settlements is the combined outcome of natural environmental constraints, socio-economic drivers, and governmental institutional regulation. This study outlines future research directions in finer-scale analysis using multi-source data, methodological innovation in mechanism analysis, and practical exploration of adaptive optimization models.The results provide a scientific basis for the layout optimization of rural settlements and territorial spatial planning in the karst areas of Southwest China.