This study aimed to investigate the additional effects of perioperative immunonutrition (IMN) compared with preoperative immunonutrition (IMN) on anthropometric, nutritional, and biochemical parameters, hospital stay and postoperative complications in patients with colorectal cancer. Oral supplementation enriched with arginine, omega-3 fatty acids, and dietary nucleotides was given to 25 patients before and after the operation (Group 2); 25 patients received the same formula before surgery and standard isocaloric nutrition following the operation (Group 1). Postoperative body weight, body mass index (BMI), and middle upper arm circumference (MUAC) of Group 1 decreased more than Group 2 during follow-up (p < 0.05). The biochemical parameters, C-reactive protein (CRP), aspartate aminotransferase (AST) and fasting plasma glucose (FPG) were higher, and albumin was lower than the baseline in Group 1 compared to Group 2 (p < 0.05). There was a negative correlation between CRP and Nutrition Risk Screening (NRS) 2002 scores, and prealbumin and NRS 2002 scores had a positive correlation (p = 0.007, r = 0.384; p = 0.012, r = 0.352). There was no difference in hospital stay and postoperative complications between the groups (p > 0.05). Perioperative immunonutrition, compared to preoperative immunonutrition, can be used as a positive and effective approach in improving some anthropometric measurements and biochemical parameters in patients undergoing colorectal cancer surgery.