In this study, it was aimed to increase added value of rice bran which is a by-product of paddy processing. Optimisation of ultrasound assisted extraction produced the highest rice bran protein yield (39.85%) with the parameters as solid/liquid ratio of 0.43, power of 48.25% amplitude, and ultrasound application time of 29.89 min. Based on the optimised solid/liquid ratio and time, antioxidant and antiproliferative properties of protein isolates treated with different level of ultrasound power were determined. Total antioxidant capacity (TEAC), 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity, total phenolic content (TPC), metal chelating activity and the effects on HepG2 cytotoxicity of rice bran protein isolates were evaluated. The highest values of TEAC (17.73%), DPPH (63.61%), TPC (297.43 mg GAE/mg), and metal chelating activity (55.34%) were obtained from samples treated with 100% ultrasound power. Th results of the study showed that the ultrasound power had significant effect (P< 0.05) on TPC, metal chelating activity, and DPPH scavenging activity of rice bran proteins.