Abstract: Objective:To investigate procalcitonin and C-reactive protein levels in diarrheal patients who underwent irinotecan che -motherapy.Methods:Procalcitonin and C reactive protein were detected among 85diarrheal and 63non-diarrheal patients after irinote -can chemotherapy. Results:According to WHO classification, patients without diarrhea are classified as grade0, whereas patients with diarrhea can be classified as grades Ⅰ- Ⅳ. In grades 0, Ⅰ, Ⅱ, Ⅲ, and Ⅳpatients, the levels of procalcitonin were 0.29± 0.17, 0.30±0.18, 0.36± 0.20, 1.24± 0.22, and 2.15± 0.26ng/mL on the second day, respectively. However, on the fourth day, the procalcitonin lev -els were 0.28± 0.15, 0.30± 0.14, 0.34± 0.18, 2.00± 0.22, and 2.40± 0.28ng/mL, respectively. Moreover, in grades 0, Ⅰ, Ⅱ, Ⅲ, and Ⅳ, the levels of C-reactive protein were 6.06± 1.85, 6.12± 1.16, 6.20± 1.68, 22.62± 4.55, and 31.26± 5.23mg/L on the second day, respectively. On the fourth day, the C-reactive protein levels were 5.80± 1.82, 5.94± 1.14, 6.15± 1.55, 30.52± 4.74, and 38.67± 5.68 mg/L, respectively. No significant difference was found between the procalcitonin and C-reactive protein levels of stages Ⅰand Ⅱpa -tients ( P>0.05), but a significant difference was found between stages Ⅰ, and Ⅱpatients and stages Ⅲand Ⅳpatients ( P<0.05). Con -clusion: Monitoring levels of procalcitonin and C- reactive protein may be helpful in the early evaluation of the severity of diarrhea. This process has prognostic effect and can be used to assess whether patients have enterogenous bacterial infection. Monitoring the lev-els of these proteins has certain clinical value and can be used to guide early anti-infection therapy.