Abstract Effects of process variables namely pH, dye concentration, adsorbent dosage, temperature, particle size and agitation speed on kinetics of methylene blue adsorption onto gulmohar plant leaf powder were investigated. Quadratic models were proposed to predict pseudo second order rate constant and equilibrium uptake in terms of the process variables. Model coefficients were determined by multiple regression analysis. Statistical tools like Student's t-test, F-test, ANOVA and lack-of-fit were used to define the most important process variables. The proposed models could predict the rate constant and equilibrium dye uptake with high R 2 values (0.94 and 0.947). It was found that rate constant increased with decrease in concentration, decrease in particle size, increase in adsorbent dosage, increase in agitation speed and increase in temperature. Meanwhile, it was found that equilibrium dye uptake increased with increase in concentration and decrease in dosage. Apart from these combined effects of the process variables were established through multiple regression analysis. Langmuir monolayer adsorption capacity of GUL was found to be 186.22 mg/g.