Biosynthesis of iron oxide nanoparticles (Fe2O3 NPs ) by Pseudomonas Aeruginosa and Bacillus Velezensis has been studied. The effects of preparation conditions on the synthesis of Fe2O3 NPs by Pseudomonas Aeruginosa and Bacillus Velezensis were studied. The process variables of preparation Fe2O3 NPs were optimized, the XRD, BET, TEM, FT-R and other characterization of Fe2O3 NPs were carried out to explore the catalytic degradation by visible light. Using methyl violet and isothiazolinone as organic pollutant models, their photocatalytic performance was explored. After 5 h of blue light irradiation, with the amount of catalyst 0. 03 g and the inhale concentration of methyl volet solution 10 mg/L, the degradation rates of methyl volet by Fe2O3@PA (prepared by P suudomonas Aerugieosa) and Fe2O3@BV (prepared by Bacillus Velezeesis ) reached 61.29% and 69.87%, respectively. When the amount of catalyst was 0.03 g, the inhale concentration of isothiazolinone solution was 30 mg/L and the pH was 5, after 4.5 h UV irradiation at pH 5, the degradation rates of Fe2O3@PA and Fe2O3@ BV to isothiazolinone reached 76.21% and 82.13%, respectively. [ABSTRACT FROM AUTHOR]