Objectives: It is of utmost importance to investigate the newly discovered immunohistochemical proteins that are helpful in differentiating various histological subtypes of endometrial carcinomas (ECs). In this study, we aimed to compare the localization and expression profile of selected proteins (ARID1A, nidogen 2 (NID2), LRH-1, and GPR30) in 60 early-staged (I and II) G2/G3 ECs with different histological subtypes. Methods: Endometrioid-type (n = 20), serous (n = 20), and clear-cell (n = 20) ECs were immunohistochemically stained applying the anti-ARID1A, -NID2, -LRH-1, and -GPR30 antibodies. Normal endometrial samples (n = 8) were selected as a control group. Results: In general, 95% (19 out of 20) and 100% (20 out of 20) of endometrioid and serous samples revealed moderately/intense cytoplasmic/nuclear ARID1A immune-positivity, while only four out of 20 (20%) clear-cell carcinomas showed moderate staining. A significant difference in ARID1A expression was noted between different histological subtypes of ECs (clear-cell cancer vs endometrioid cancer, p 0.001, and clear-cell cancer vs serous cancer, p 0.001). Cytoplasmic NID2 staining did not differ significantly between histological subtypes. Most of the endometrioid (19/20; 95%) and serous (19/20, 95%) neoplasms revealed intense cytoplasmic LRH1-immunopositivity. Weak/moderate GPR30 cytoplasmic reactivity was detected in 16 out of 20 (80%) endometrioid EC, however, this protein was neither noted in clear-cell and serous neoplasms nor normal endometria. Differences in GPR30 immunoreactivity between endometrioid cancer and serous/clear-cell cancer were of significant values (p 0.005). Conclusion: Weak ARID1A expression may be associated with gene alterations in selected EC histological subtypes. GPR30 staining may help to differentiate various histological EC subtypes.