A field experiment was conducted in a clayey soil at the experimental farm of the Faculty of Agric. El-Mansoura Univ.to study the effect of sulpher (S) application and Dicyandiamide, (DCD) comparing with mineral fertilization of NPK rates on chemical composition of lettuce plant (Lactuca sativa L.) in factorial design. Experiment included 9 treatments which were 3 rates of NPK fertilization (50, 75 and 100% from recommended dose) and 3 treatments of (DCD, S and DCD + S) with 3 replicates. Thus, the total number of the experimental plots was 27 plots.Results indicated that chlorophyll content, N, P, K and S concentrations, NO₃-N and NO₂-N content mg.l^-1 as well as available N, P and K mg.l^-1 in leaves were significantly increased due to increasing NPK fertilization rates, and the highest mean values were recorded with adding 100% NPK from recommended dose, while nitrate reducates activity was decreased. The highest average values of mentioned parameters indicated that using mix of (S & DCD) comparing with other treatments except NO₃-N, and NO₂-N mg.l^-1 which recorded with adding sulphur. In the same time the effect of interaction among treatments on the traits illustrated that the highest values of all parameters in lettuce were connected with 100% NPK + S + DCD. While, nitrate reducates activity of lettuce recorded the highest mean values with S+DCD+ 50% NPK over the control