The effects of stand density on soil nutrients and enzyme activities were studied through investigating typical plots of Pinus massoniana plantation in the hilly red soil region in southern China. Pinus massoniana plantation of middle stand density (1 560 tree/hm2) had higher levels of soil organic matter, total nitrogen, total potassium, exchangeable calcium and exchangeable magnesium but with the most serious soil acidification phenomenon. At the same time, also had higher soil invertase, urease and polyphenoloxidase activities in Pinus massoniana plantation of 1 560 tree/hm2. But soil catalase activity was lowest in the Pinus massoniana plantation of middle stand density. Soil acid phosphatase activity did not respond obviously to the variation of stand density. Therefore, Pinus massoniana plantation with appropriate stand density can improve soil fertility and soil enzyme activities to some extent in the study region.