Aims: Malnutrition increases postoperative risk in head and neck cancer (HNC) reconstructive surgery. Neoadjuvant chemotherapy (NAC) is frequently administered during the surgical waiting period, but its impact on nutritional and inflammatory deterioration remains unclear. We evaluated the impact of NAC on changes in nutritional status during the waiting period. Methodology: We retrospectively reviewed 91 patients with oral cavity, oropharyngeal, hypopharyngeal, or laryngeal cancer who underwent reconstructive surgery between 2014 and 2023. Sixty received NAC and 31 did not. Changes in body mass index (BMI), serum albumin, hemoglobin, lymphocyte count, modified Glasgow Prognostic Score (mGPS), and major postoperative complications (Clavien–Dindo grade ≥3) were analyzed according to the NAC status. Results: The mean waiting period was significantly longer in the NAC group (59 vs. 31 days, p<0.001). During the waiting period, BMI, albumin, and hemoglobin decreased (all p<0.001), while lymphocyte count decreased and mGPS increased (both p<0.05) in both groups. Declines in BMI (0.66 vs. 0.32, p=0.18), albumin (0.51 vs. 0.48, p=0.79), lymphocyte count (−136 vs. −70/μL, n.s.), and mGPS (+0.33 vs. −0.06, n.s.) did not differ between the groups. Hemoglobin decrease was greater in the NAC group (1.85 vs. 0.90 g/dL, p<0.05). Major complication rates did not differ between the groups. Conclusion: Nutritional and inflammatory status deteriorated during the surgical waiting period in HNC patients. Although NAC prolonged waiting time and was associated with greater hemoglobin decrease, it did not significantly worsen overall nutritional status or increase major postoperative complications.