Abstract: The combined effect of different rates of fertilizer (N + P) and concentrations of a growth regulator commercial product on growth and yield of cotton was studied. There were two types of treatments viz. fertilizer rates (F) and Mixtalol concentrations (M) placed randomly in the field under split-splot design with four replications. Main-plot treatments were: Fo Control/no fertilizer), F1 (half rate of recommended N and P fertilizers viz. 575 and 28.8 kg ha-1, respectively) and F2 (full rate of recommended N and P fertilizers viz. 115 and 57.5 kg ha-1, respectively). The sub-plot treatments included: Mo (Control/no Mixtalol Spray), M1 (2 pm Mixtalol sprays thrice) and M2 (3 ppm Mixtalol spray thrice). Thus there were nine treatments combinations in total. Data on plant height and number of branches per plant showed significantly increased values of these two with the both doses of fertilizer as well as Mixtalol over Control. The difference between M1 and M2 was non significant for both parameters, while the F1 and F2 gave statistically similar values for number of branches and F2 was superior to F1 with respect to plant height. The best combination was F2 x M1 and the lowest values were found in Fo x Mo. As regards the number of bolls per plant and seed cotton yield, F2 gave statistically better results than did F1 and F2. among Mixtalol treatments M1 performed better than M2. the synergistic effect was best with F2 x M1 and it was lowest at Fo x Mo. Thus it was concluded that cotton gave the highest response to full rate of fertilizer (F2) along with lower concentration (2 ppm) sprays Mixtalol (M1) as the most suitable combination.