Relapsed/refractory ovarian cancer, especially platinum resistance recurrence, remains a major therapeutic challenge. Here, we present the case of a patient with recurrent ovarian clear cell carcinoma (OCCC) who failed to respond to multiline chemotherapy and target therapy but achieved an immune complete response (iCR) with programmed cell death 1 (PD-1) inhibitor treatment. The overall survival (OS) was 59 months, and the recurrence-free survival (RFS) was 34 months after immunotherapy, which was counting. Meantime, molecular testing results revealed that traditional biomarkers for immunotherapy, including PD-L1 expression, microsatellite instability (MSI), and tumor mutational burden (TMB), were negative. HLA-B44 (B*18:01) supertype was confirmed by sequence-based HLA typing. This case raises the possibility that ovarian cancer patients with multidrug resistance may still benefit from PD-1 inhibitor therapy, even if PD-L1 pathology is negative.