Objective To investigate the expression of human chorionic gonadotropin beta subunit (CGB) mRNA and gonadotropin-releasing hormone type 1 (GnRH1) mRNA in the serum of the patients with gestational trophoblastic tumor, and to explore the relationships of the expressions of CGB mRNA and GnRH1 mRNA with metastasis, and the possible markers of early hematogenous metastasis. Methods Fifty-two pregnant women with gestational trophoblastic tumor and 21 patients with hydatidiform mole were selected. Twenty normal pregnant women and twenty non-pregnant women were selected as controls. Clinical data and peripheral blood of all participants were collected. The serum levels of CGB mRNA and GnRH1 mRNA in the four groups were detected by RT-PCR, and their relationships with clinical indicators of early metastasis were analyzed. Results The expressions of CGB mRNA and GnRH1 mRNA in serum of the patients with gestational trophoblastic tumor were higher than those of the other three groups. The expression of CGB mRNA was not related to age, tumor size, or previous pregnancy status, but was correlated with distant metastasis, number of metastatic foci, clinical FIGO stage and prognosis. The expression of GnRH1 mRNA in the patients with gestational trophoblastic tumor was not related to age, tumor size, number of metastatic foci or previous pregnancy status, but was related to distant metastasis, clinical FIGO stage and prognosis. Conclusions Serum CGB mRNA and GnRH1 mRNA expressions increase in the patients with gestational trophoblastic tumor and are correlated to metastasis-related clinical indicators. Therefore, CGB and GnRH1 may be useful markers for assessing the early hematogenous metastasis of gestational trophoblastic tumor.