Abstract: OBJECTIVE To explore the clinical value of C-reactive protein (CRP) in diagnosis of patients with tumor or infectious diseases so as to provide guidance for clinical diagnosis. METHODS A total of 80 patients with tumor and infectious diseases who were treated in hospitals from Jan 2015 to Sep 2015 were enrolled in the study and assigned as the experimental group, meanwhile, 61 healthy people who received the physical examination were set as the control group. The CRP level of all the study objects was quantitatively detected by using nephelometry, the procalcitonin level was detected by means of German BRAHMS GM bH procalcitonin assay kit, and the value of CRP in the diagnosis of the patients with tumor and infectious diseases was evaluated. RESULTS The levels of CRP and procalcitonin of the experimental group were significantly higher than those of the control group. The positive rate of CRP of the experimental group was 23.75%, significantly higher than 4.92% of the control group; the positive rate of CRP varied in the patients with different types of tumors and infectious diseases; the higher the degree of malignancy, the higher the positive rate of CRP was, and there was significant difference (P<0.05). The positive rate of CRP of the patients with tumors and infectious diseases was decreased to some extent after the treatment. CONCLUSION The dynamic detection of CRP can achieve ideal effect on diagnosis of the patients with tumors and infectious diseases, of which the diagnosis rate is significantly higher than that of the procalcitonin; the CRP combined with procalcitonin may raise the clinical diagnosis rate.