© Mary Ann Liebert, Inc. A serosurvey was undertaken in 15 locations in the midwest to southwest of Western Australia (WA) to investigate the seroprevalence of Ross River virus (RRV) neutralizing antibodies and factors associated with infection in western grey kangaroos (Macropus fuliginosus). The estimated seroprevalence in 2632 kangaroo samples, using a serum neutralization test, was 43.9% (95% CI 42.0, 45.8). Location was significantly associated with seroprevalence (p <0.001). There was a strong positive correlation between seroprevalence and the average log-transformed neutralizing antibody titer (r = 0.98, p <0.001). The seroprevalence among adult kangaroos was significantly higher than in subadult kangaroos (p <0.05). No significant association was observed between seroprevalence and the sex of kangaroos (p > 0.05). The results of this study indicate that kangaroos in WA are regularly infected with RRV and may be involved in the maintenance and transmission of RRV.