To compare recommendations across international guidelines on fertility-sparing surgery (FSS) for borderline and malignant ovarian tumors. A systematic literature search in PubMed and five major oncology organization websites was conducted for the identification of relevant guidelines, and data on FSS issue were extracted and compared. In total, 7 guidelines (NCCN, ESGO-ESHRE-ESGE, BGCS, SEOM-GEICO, ESGO-ESMO-ESP, ESMO, and LGSOC-consensus) were included in final analysis. The guidelines unanimously recommend ascites/peritoneal lavage cytology, omentectomy/omental biopsy, and random peritoneal biopsy for staging borderline and malignant ovarian tumors. However, discrepancies emerged regarding the necessity of lymphadenectomy, appendectomy, and endometrial evaluation in different histologic subtypes. Not all guidelines address FSS eligibility, and controversy exists. Only three guidelines (NCCN/BGCS/ESGO-ESHRE-ESGE) provide recommendations for post-childbearing completion surgery in patients receiving FSS. For BOTs, NCCN guideline recommends routine post-childbearing completion surgery, while ESGO-ESHRE-ESGE guideline advises against it, and BGCS guideline advocates individualization. For MGCTs, both NCCN and BGCS guidelines recommend routine post-childbearing completion surgery, whereas ESGO-ESHRE-ESGE guideline recommends against it. For EOCs and MSCSTs, NCCN guideline recommends to consider routine completion surgery after finishing childbearing. In contrast, ESGO-ESHRE-ESGE guideline only recommends that patients with a family history of genetic high-risk EOCs and patients with granulosa cell tumors undergo completion surgery, while individualized management should be applied to other EOC and MSCST patients. Interguideline variability exists in FSS recommendations in borderline and malignant ovarian tumors, and harmonizing evidence-based criteria for FSS is critical to optimize fertility preservation without compromising oncologic outcomes in these populations.