Background: Endometrioid (EEOC), clear cell (OCCC) or mucinous ovarian cancer (MOC) had the highest incidence of Less Common Ovarian Cancers (LCOC). The benefit of adjuvant chemotherapy, lymphadenectomy or fertility-sparing surgery (FSS) for Stage I of these rare cancers remains unclear. Methods: We conducted a retrospective case-controlled study examining the Surveillance, Epidemiology, and End Result (SEER) database between 2000 and 2016. Propensity score matching is used to avoid the selection bias caused by the heterogeneity of demographic and clinical characteristics. Adjuvant chemotherapy or lymphadenectomy or fertility-sparing surgery on overall survival (OS) was compared with log-rank tests. A univariate and multivariate Cox analysis was performed to control for confounders. A nomogram was developed and the discriminatory ability of the model was analyzed. Results: The study identified 4,681 patients with FIGO stage I EEOC, 2,450 with stage I OCCC, and 2,839 with stage I MOC. After the propensity score matching, there was an equally comparable number of patients with or without adjuvant chemotherapy. The results showed that adjuvant chemotherapy could not prolong the 5-year OS of patients with stage I OCCC (86.7% vs. 85.9%, p = 0.732) and MOC (87.6% vs. 88.2%, p = 0.843). Adjuvant chemotherapy was associated with a 5-year OS benefit only in the subgroup of patients with substage IC, grade 3 EEOC (85.2% vs. 67.7%, p = 0.008). We also found that lymphadenectomy improved the 5-year OS of stage I EEOC (93.5% vs. 86.3%, P = 0.000), OCCC (87.8% vs. 82.8%, P = 0.040) and MOC patients (91.8% vs. 84.2%, P = 0.000). Furthermore, we observed that the 5-year OS raised in stage I EEOC (91.9%vs. 87.7%, P = 0.029) and OCCC (87.6% vs. 81.3%, P = 0.051) patients when conducted the non-fertility-sparing surgery (non-FSS) rather than the FSS. However, FSS did not significantly impact the 5-year OS of MOC patients (91.3% vs. 88.8%, P = 0.181). The nomogram survival prediction model showed that the area under the receiver operating characteristic (ROC) curve (AUC) was 0.650, 0.640 and 0.710 in EEOC, OCCC and MOC, respectively. The C-indexes for the OS were 0.666 (95%CI:0.638-0.694), 0.613 (95% CI:0.575-0.650) and 0.677 (95% CI:0.637-0.716), respectively. Conclusions: Adjuvant chemotherapy was associated with a 5-year OS benefit for patients with stage IC, grade 3 EEOC, but it was unnecessary for patients with stage I OCCC and MOC. Lymphadenectomy was associated with a survival benefit for these early cancer patients. FSS is appropriate for stage I MOC but needs to be discussed for stage I EEOC and OCCC. We constructed predictive nomograms to evaluate the OS of patients with stage I EEOC, OCCC or MOC, and it will provide an individualized evaluation of OS for suitable treatments.