Objectives: To compare tumor necrosis factor receptor 1 (TNFR1) protein expression in women with unexplained early spontaneous abortion (UESA) and normal pregnancy. Methods: In a prospective study, 62 women with UESA and 60 with normal pregnancy were studied. Decidual membrane TNFR1 was detected by flow cytometry and immunohistochemistry, and serum soluble TNFR1 were by ELISA. Statistical analyses of resulting data employed the student's t test, the Fisher's Exact, and the nonparametric Wilcoxon test. Results: The percentage of membrane tumor necrosis factor receptor 1 (mTNFR1) positive decidual cells was 16.42F7.1 for women with UESA and 12.47F5.3 for women with normal pregnancy (pb0.05). The number of mTNFR1 positive cells was more in decidual stromal and vessel endothelial cells in women with UESA, and serum soluble tumor necrosis factor receptor 1 (sTNFR1) concentration was significantly higher than in women with normal pregnancy (554.56F126.7pg/ml vs. 175.3F52.4pg/ml; pb0.001). Conclusion: The overexpression of TNFR1 may contribute to the development of ESA.