Palm oil slurry and palm kernel cake are the products of oil processing waste. This study aims to investigate the ability of three strains of Rhizopus microsporus (UICC 500, UICC 531 and UICC 539) to grow and ferment the non-sterile and sterile slurry and kernel cake mixtures (3:1). The total weight of the waste mixtures was 20 g with inoculum concentration of 10% (v/w), and the initial cell number was 1 × 107 CFU/mL. Fermentation was carried out for five days at 28°C. Only Rhizopus microsporus UICC 539 was able to grow and ferment on both the non-sterile and sterile mixtures. Rhizopus microsporus UICC 500 and UICC 531 were able to grow and ferment only on sterile mixtures. On the sterile mixtures, Rhizopus microsporus UICC 539 showed the fastest growth and attained the highest cell number (1.77 × 108 CFU/mL), followed by Rhizopus microsporus UICC 531 (1.35 × 108 CFU/mL), and Rhizopus microsporus UICC 500 (1.3 × 108 CFU/mL). This study showed that all R. microsporus strains have the ability to grow and ferment agro-industrial waste such as palm oil processing waste. Rhizopus microsporus UICC 539 is a potential strain to ferment non-sterile and sterile mixtures of slurry and palm kernel cake. Further study is required to determine the effect of fermentation by R. microsporus on the nutrient content of palm oil waste.