Background: The ability of pretreatment laboratory markers of acute-phase inflammatory reactions like serum albumin level (SAL), hemoglobin (Hb), and absolute blood cell counts to predict complete pathological response (CPR) to neoadjuvant chemoradiotherapy (NACRT) in patients with locally advanced rectal cancer (LARC) has not yet been fully studied. Methods: We retrospectively examined the relation between SAL, Hb and absolute blood cell counts, and CPR rates in 140 LARC patients treated with NACRT. Results: Univariate analysis showed a significantly higher probability of CPR to NACRT in patients with clinical stage (CS) III LARC who had SAL >3.5 mg/dl (OR = 2.39; p = 0.04) and a neutrophil-to-lymphocyte ratio (NLR) value <5 (OR = 2.86; p = 0.03). The relation of CPR with SAL (OR = 2.11; p = 0.048) and NLR (OR = 2.54; p = 0.04) was confirmed by multivariate analysis in the same subset of patients. None of the parameters studied predicted CPR in patients with CS II disease. Patients who achieved CPR to NACRT had a higher probability of 5-year overall survival (HR 0.48; p = 0.01) and 5-year disease-free survival (HR 0.33; p = 0.003). Conclusions: Our data indicate that SAL >3.5 mg/dl and NLR <5 may be positively related to CPR after NACRT in patients with CS III LARC. Hypoalbuminemia and a high NLR may be considered an indication for a more aggressive approach to NACRT and postoperative adjuvant chemotherapy in this subset of patients. This hypothesis requires confirmation in a randomized study.