Abstract: By isotope tracer technique, experiments of SPECT and biodistribution on nude mice bearing tumor are performed to explore whether folate conjugated penicillin G amidase (F PGA) has the ability of targeting to folate receptor positive solid tumors, which will be helpful to establish a base for further targeting therapies. The results showed that the labeling efficiencies of  125 I F PGA and  125 I PGA are 90%, and their radiochemical purities are more than 95% after purified, with suitable stabilities both in vivo and in vitro. At 4~24 h postinjection, the appreciable radioactivity accumulation at tumor position can be obtained from SPECT images of  125 I F PGA administered group, however which is not seen in the contrast group of  125 I PGA at any time. The radioactivity ratio of tumor to muscle (T/M) of  125 I F PGA is obviously higher than that of the contrast( F=13.38， P =0.014 6).  125 I F PGA is quickly cleared from non targeted sites. It indicated that by folate receptor pathway, F PGA can specially target to folate receptor positive SKOV3 solid tumors in vivo, with good feature of target to non target tissues, and it may be an ideal agent for targeting therapies.