Background: Liquid-based cytology (LBC) offers an alternative method to biopsy in screening endometrial cancer. Cell block (CB), prepared by collecting residual cytological specimen, represents a novel method to supplement the diagnosis of endometrial cytology. This study aimed to compare the specimen adequacy and diagnostic accuracy of LBC and CB in the diagnosis of endometrial lesions. Methods: A total of 198 women with high risks of endometrial carcinoma (EC) from May 2014 to April 2015 were enrolled in this study. The cytological specimens were collected by the endometrial sampler (SAP-1) followed by histopathologic evaluation of dilatation and curettage or biopsy guided by hysteroscopy. The residual cytological specimens were processed into paraffin-embedded CB after LBC preparation. Diagnostic accuracies of LBC and CB for detecting endometrial lesions were correlated with histological diagnoses. Chi-square test was used to compare the specimen adequacies of LBC and CB. Results: The specimen inadequate rate of CB was significantly higher than that of LBC (22.2% versus 7.1%, P < 0.01). There were 144 cases with adequate specimens for LBC and CB preparation. Among them, 29 cases were atypical endometrial hyperplasia (11 cases) or carcinoma (18 cases) confirmed by histology evaluation. Taking atypical hyperplasia and carcinoma as positive, the diagnostic accuracy of CB was 95.1% while it was 93.8% in LBC. When combined LBC with CB, the diagnostic accuracy was improved to 95.8%, with a sensitivity of 89.7% and specificity of 97.4%. Conclusions: CB is a feasible and reproducible adjuvant method for screening endometrial lesions. A combination of CB and LBC can improve the diagnostic accuracy of endometrial lesions.