Introduction. Many body systems, especially the immune system, are affected by circadian rhythm disorders (CRDs). This study investigated the effects of shift lag on wound healing and bowel anastomosis in rats. Materials and Methods. Forty-five rats were randomly divided into 3 groups: placebo, control, and experimental. Circadian rhythm was disturbed with altered light/dark cycles. Colon anastomosis was performed in rats with and without disturbed circadian rhythms. Serum melatonin levels and bowel anastomosis bursting pressures were measured. Tissue samples were used to measure tissue hydroxyproline levels and for histological assessment. Results. In the groups with an altered circadian rhythm, the bowel bursting pressures, tissue hydroxyproline levels, and fibrosis were greater than the control group. Conclusion. This study found that a CRD, simulated by altered light/dark cycles, positively affected the anastomotic bursting pressure. This suggests that cytokines such as interleukin (IL)-1, IL-6, transforming growth factor a, and stress hormones affect fibroblasts and thereby increase collagen synthesis in the proliferative phase. More studies are necessary to understand the effects of CR Ds.