Field experiments were conducted to determine the effect of sulfur (S) and Nitrogen (N) on nitrate reductase (NR) and ATP. sulfurylase activities in groundnut cultivars (Arachis hypogea L. cv. Ambar and Kaushal). Two combinations of S (in kg $ha^{-1}$): 0S (-S) and 20S (+S) were used with $20kg;ha^{-1}$ N. The application of S enhanced the NR and ATP-sulfurylase activities in both the cultivars at all the growth stages. The application of 5 also increased soluble protein and chlorophyll content in the all growth stages of both the cultivars. NR and ATP-sulfurylase activities in the leaves were measured at various growth stages as the two enzymes catalyze the rate limiting steps of the assimilatory pathways of nitrate and sulfate, respectively.