Previous studies have shown that albumin-related systemic inflammation is associated with the long-term prognosis of cancer, but the clinical significance of an early (≤ 7 days) post-operative serum albumin level has not been well-documented as a prognostic factor in patients with renal cell cancer. We retrospectively included patients hospitalized for kidney cancer from January 2009 to May 2014. First, the receiver operating characteristic analysis was used to define the best cut-off of an early post-operative serum albumin level in determining the prognosis, from which survival analysis was performed. A total of 329 patients were included. The median duration of follow-up was 54.8 months. Patients with an early post-operative serum albumin level < 32 g/L had a significantly shorter median recurrence-free survival (RFS; 49.1 versus 56.5 months, P = 0.001) and median overall survival (OS; 52.2 versus 57.0 months, P = 0.049) than patients with an early post-operative serum albumin level ≥ 32 g/L. After adjusting for age, BMI, tumor stage, post-operative hemoglobin concentration, and pre-operative albumin, globulin, and hemoglobin levels, multivariate Cox regression showed that an early post-operative serum albumin level < 32 g/L was an independent prognostic factor associated with a decreased RFS (HR = 3.60; 95% CI,1.05-12.42 [months], P = 0.042) and decreased OS (HR = 9.95; 95% CI, 1.81-54.80 [months], P = 0.008). An early post-operative serum albumin level < 32 g/L is an independent prognostic factor leading to an unfavorable RFS and OS. Prospective trials and further studies involving additional patients are warranted.