This study aimed to evaluate the effects of by-product molasses and waste orange peels (WOP) as the nutrient medium on lipase production with Rhizopus arrhizus NRRL 2286 and investigate the inductive effect of waste cooking oil (WCO) on activity. The results showed that the highest specific growth rate and the maximum biomass concentration were obtained 0.424 hL1 and 3.83 g dry weight/L for 70 g/L WOP, respectively. Additionally, the highest intracellular and extracellular lipase activities were attained in 50 g/L WOP as 400 U/g and 13.2 U/mL, correspondingly. Next, the inductive effects of WCO and olive oil were tested in lipase production. Intracellular lipase activity enhanced and reached a maximum of 520 U/g in the presence of 10 g/L WCO with an increase of 30% compared to the one without WCO. However, both inducers caused a diminish in extracellular lipase hydrolysis activity. Overall, this study reveals that the lipase production of R. arrhizus can be accomplished using WOP and WCO with the optimum conditions. (c) 2021, The Society for Biotechnology, Japan. All rights reserved.