Background and Objectives: Ovarian cancer, including tubal and peritoneal cancer, is the third most common gynecological cancer and the leading cause of death from gynecological malignancies in developed countries. This study explores the prognostic value of the neutrophil-to-lymphocyte ratio (NLR) in determining the optimal duration of neoadjuvant chemotherapy (NACT) for advanced ovarian cancer. It also investigates the correlation between NLR dynamics and the KELIM score, a chemosensitivity marker, to enhance individualized therapeutic strategies. Materials and Methods: A total of 79 patients underwent NACT followed by interval debulking surgery (IDS) or palliative care. The data collected included demographic information, tumor characteristics, treatment modalities, and laboratory parameters. The baseline NLR (NLR-T0) and post-therapeutic NLR (NLR-T1) were calculated, and their variation (NLR∆) was analyzed. The KELIM score was determined using CA-125 values. Results: Patients with a high baseline NLR (≥2.5) had significantly worse progression-free survival (PFS) and overall survival (OS) compared to those with a low NLR (<2.5). A negative NLR∆ was associated with poorer PFS and OS. The KELIM score indicated a more effective treatment response, with higher scores correlating with better outcomes. The majority of patients achieved R0 resection, and those with favorable KELIM scores showed improved survival rates. Conclusions: The NLR is a valuable prognostic marker for assessing treatment response and guiding NACT duration in advanced ovarian cancer.