A field experiment was conducted to study the effects of straw returning timing combined with nitrogen (N) fertilizer application ratio on enzyme activities in paddy soil in order to provide theoretical basis for fostering soil fertility and stabilizing paddy field ecosystem function. The experiment consisted of two rice straw returning times (W_S: returning in winter; S_S: returning in spring) and four N fertilizer application levels (N₀, straw returning and no N fertilization during all the course; N_B, conventional fertilization, and no N fertilization when straw returning; N_30B, 30% N of base fertilizer applied when straw returning; N_60B, 60% N of base fertilizer applied when straw returning). The results showed that: 1) Straw returning in winter increased the activities of six soil enzymes (β-Glucosidase, β-Cellobiosidase, β-Xylosidase, Phenol oxidase, Peroxidase and Invertase) related to C turnover. In winter fallow period, enzyme activities were higher at winter straw returning than those at spring straw returning, and winter straw returning increased both the activities of β-Glucosidase and Peroxidase during early-rice growth stage. 2) Rice straw returning combined with N fertilization application significantly increased β-cellobiosidase activity both in winter fallow period and in early-rice growth stage, but there was no significant difference in soil enzyme activities under the three levels of N fertilizer application. 3) All the enzyme activities, except Phenol oxidase, had significantly positive correlations with organic C inputs. Therefore, rice straw returning combined with N fertilizer application in winter can regulate soil enzyme activities related to C turnover to some extent, which has ecological significance to promoting straw returning in winter and ensuring the crop yield.