Introduction: In Japan, the direct smearing preparation (conventional preparation) has been widely used for cytological examination of the endometrium. Problems with the conventional preparation can be dissolved by liquid-based cytology (LBC) preparation. The Yokohama System is a method for reporting endometrial cytology, but the system lumps cancers together and does not distinguish between histological types. The objective of this study was to clarify morphometrical differences among endometrial endometrioid carcinoma grade 1 (G1), grade 3 (G3), and serous carcinoma (Serous) by image analysis of endometrial LBC. Methods: Using Papanicolaou smears prepared by LBC after sampling with a brush from 32 G1, 16 G3, and 16 Serous patients, image analysis was performed concerning the following 11 items: (1) number of layers of cluster, (2) area of cluster, (3) perimeter of cluster, (4) roundness of cluster, (5) complexity of cluster, (6) area of nucleus, (7) perimeter of nucleus, (8) roundness of nucleus, (9) complexity of nucleus, (10) area of nucleolus, and (11) nucleolus/nucleus (N/N) ratio. The data were statistically compared among G1, G3, and Serous. Results: Significant differences were observed in the number of layers of cluster (G1<G3<Serous), area of cluster (G1>G3<Serous), area of nucleus (G1<G3<Serous), area of nucleolus (G1<G3<Serous), roundness of cluster (G1>G3, G1>Serous), complexity of cluster (G1<G3, G1<Serous), roundness of nucleus (G1<Serous), complexity of nucleus (G1>Serous), and N/N ratio (G1>G3, G3<Serous). Conclusion: The number of layers and area of cluster, complexity of cluster, area and complexity of nucleus, area of nucleolus, and N/N ratio were suggested to be useful for the differentiation of histological types among G1, G3, and Serous. Particularly, differences in the number of layers of cluster, size of nucleus, and size of nucleolus among histological types were large and are considered to be potentially effective points of differential diagnosis.