Abstract:The characteristics of soil nutrients in primary and secondary forests of Mulun Karst forest of Guangxi, China were studied, and the contents of SOM, N, P and K at 0~5 cm depth soil from the three main landforms, such as steep slope, gentle slope and depression, were detected, each including rock-soil (shallow and scattered soil) and soil surface microhabitat (relatively thick and continuous soil). The results showed that the contents of SOM, TN and AN were high in primary forest with high species diversity, with 345 g kg-1 of SOM in rock-soil surface microhabitat of gentle slope, while above 80 g kg-1 in soil surface microhabitat of depression. However, those decreased in secondary forest dominated by Alchornea trewioides, Mallotus conspuyrcatus, Eurycorymbus cavaleriei with lower species diversity. The SOM contents in rock-soil (110 g kg-1) and soil surface microhabitat (77 g kg-1) in gentle slope decreased significantly, which were only 32% and 35% of that in primary forest, respectively; but there were not significant differences in SOM, TN and AN contents in depression between the two vegetations. There were not obvious regularities in TP, AP, TK and AK contents between the two vegetations. The soil nutrient contents (except for TK) raged in order: gentle slope > steep slope > depression, but there were not significant differences among the three landforms in secondary forest. The soil nutrient contents (besides TK) in rock-soil surface microhabitat were higher than that in soil surface microhabitat.