Rubrivivax gelatinosus has the potential of biomass resource recycling combined with sewage purification. However, low biomass production and yield restricts the potential for sewage purification. Thus, this research investigated the improvement of biomass production and yield and organics reduction by Fe(3+) in R. gelatinosus wastewater treatment. Results showed that 10-30 mg/L Fe(3+) improved biomass yield in wastewater to a level found in culture medium. With optimal dosage (20 mg/L), biomass production reached 4,300 mg/L, which was 1.67 times that of the control group. Biomass yield was improved by 43.3%. Chemical oxygen demand (COD) removal reached above 91%. Hydraulic retention time was shortened by 25%. Mechanism analysis indicated that Fe(3+) enhanced the succinate and NADH dehydrogenase activities and, bacteriochlorophyll content in three energy metabolism pathways. These effects then enhanced adenosine triphosphate (ATP) production, which led to more biomass accumulation and COD removal. With 20 mg/L Fe(2+) dosage, succinate and NADH dehydrogenase, coproporphyrinogen III oxidase activities, bacteriochlorophyll content and ATP production were improved, respectively, by 48.4, 50.8, 50, 67 and 56% compared to those of the control group.