Whether morphine used in human cancer surgery would exert tumor-promoting effects is unclear. This study aimed to investigate the effects of morphine dose on cancer prognosis after colorectal cancer (CRC) resection.In a retrospective study, 1248 patients with stage I through IV CRC undergoing primary tumor resections and using intravenous patient-controlled analgesia for acute surgical pain at a tertiary center between October 2005 and December 2014 were evaluated through August 2016. Progression-free survival (PFS) and overall survival (OS) were analyzed using proportional hazards regression models.Multivariable analysis demonstrated no dose-dependent association between the amount of morphine dose and PFS (adjusted hazard ratio, HR = 1.31, 95% confidence interval, CI = 0.85-2.03) or OS (adjusted HR = 0.86, 95% CI = 0.47-1.55). Patients were further classified into the high-dose and low-dose groups by the median of morphine consumption (49.7 mg), and the morphine doses were mean 75.5 ± standard deviation 28.8 mg and 30.1 ± 12.4 mg in high-dose and low-dose groups, respectively. Multivariable models showed no significant difference in PFS or OS between groups, either (adjusted HR = 1.24, 95% CI = 0.97-1.58 for PFS; adjusted HR = 1.01, 95% CI = 0.71-1.43 for OS).Our results did not support a definite association between postoperative morphine consumption and cancer progression or all-cause mortality in patients following CRC resection.