Objective to investigate the infection status of STLV-1 in Macaca mulatta so as to decrease the infection ratio of STLV-1 effectively. Method:Monkey sera were tested with STLV-1 ELISA. Results 103 sera were STLV-1 antibody positive, and 19 sera were STLV-1 antibody equivocal, the others were STLV-1 antibody negative in 2455 sera sent to BioReliance Co. for STLV-1 antibody test. Conclusion STLV-1 average infection ratio in Macaca mulatta is 4.97%, of which, that in cynomolgus monkey is 5.4%, twice of that in rhesus monkey, STLV-1 infection ratio in Macaca mulatta increases with age.