Abstract: The effects of four NK treatments on nitrate reductase(NR)activity ,nitrate ni-trogen(NO3-N)content of leaves and curd yield in cauliflower were studied.The results in-dicated that N8K10 treatment resulted in better plant growth ,the highest curd yield and perunit leaf area curd productivity as compared with the other treatments which decreased inthe order of N8K5,N16K10,N16K5.The NR activity in leaves was higher during the curd for-mation ,while lower before flower bud differentiation and at curd harvest.The NR activityin leaves increased gradually form low to high nodes.The change trends of NO3-N contentof leaves were the same as the NR activity NK interaction caused marked effects on NR ac-tivity and NO3-N content of leaves.High N treatment could promote NR activity and de-crease NO3-N content.When N level was lowet , high K treatment could enhance NR ac-tivity and decrease NO3-N content.When N level was higher,high K treatment could de-crease NR activity and increase NO3-N content. There were no significant correlation be-tween NR activity in leaves of various growth period and curd yield.