Abstract: Objective　To evaluate the diagnostic value of the common test parameters in acute fever without obvious infection focus and sick appearance in children under 5 years. Methods　The hospitalized children with fever duration less than 7 days, anal temperature higher than or equal to 38°C, age younger than or equal to 5 years, and without obvious infection focus and sick appearance were recruited, we investigated the diagnosis value of common test parameters including C-reactive protein (CRP), procalcitonin (PCT), the white blood cell count (WBC), and neutrophil percentage (N%) , according to the final diagnostic. Results　Of 228 children, 42 children (18.42%) had serious diseases, the difference of CRP, PCT between serious diseases group and non-serious diseases group were statistically significant (P<0.001). The diagnostic cut-off point of CRP was 67.1 mg/L by specificity of 0.810 and sensitivity of 0.715, that of PCT was 0.505 ng/L by specificity 0.762 and sensitivity 0.672. The specificity and sensitivity combining CRP with PCT was respectively 0.918 and 0.617. Of 228 children, 32 children had viral infections, 40 children had bacterial infections, 15 children had mycoplasma infections. The difference of CRP, PCT, WBC, and N% among three groups were statistically significant (P<0.01)。The cut-off point of CRP was 38 mg/L by sensitivity 0.900 and specificity 0.813, that of PCT was 0.450 ng/L by sensitivity 0.700 and specificity 0.812, and the specificity and sensitivity combining CRP with PCT was respectively 0.965 and 0.630, to distinguish bacterial infections from viral infections. The diagnostic cutoff point of CRP was 80.75 mg/L by sensitivity 0.700 and specificity 0.933 distinguishing bacterial infections from mycoplasma infections. Conclusions　The parameters CRP and PCT have the diagnostic value for the children with the acute fever and age younger than or equal to 5 years and without obvious infection focus and sick appearance in etiology and serious diseases, especially the value of combining CRP with PCT is better.