Purpose To analyze the high-frequency sonographic images of lymph nodes in mesenteric lymphadenitis of different ages. Materials and Methods 139 children with mesenteric lymphadenitis (study group) and 60 normal children (control group) were divided into 1 to 5 years, 6 to 10 years and 11 to 15 years group, the characteristics of high-frequency ultrasound sonographic images were analyzed, accuracy of longitudinal diameter (L), transverse diameter (S), aspect ratio (L/S) and color Doppler blood flow signal classification for the prediction of mesenteric lymph nodes swelling were evaluated using receiver operating characteristic (ROC) curve. Results Mesenteric lymph nodes in the control group appeared as spindle shape with sparse blood flow signals, L, and L/S increased with age increasing (F=4.047, 9.586;P<0.05). Mesenteric lymph nodes in the study group displayed as oval or teardrop-shaped with rich blood flow signals, L, S and L/S did not change significantly with age increasing (F=0.184, 1.084, 2.083; P>0.05). Compared with the control group, blood flow signals were more abundant in all age groups of the study group, L and S were also significantly higher (L:t=-13.798,-12.813,-8.089;S:t= -8.212,-13.172,-9.606, P<0.01), only in the 1 to 5 years group statistically significant difference (t=-3.208, P<0.05) was showed between the two groups. From 1 to 5 years, the sensitivity and specificity for the judgment of lymph node swelling were 95.56%and 100.00%, respectively when using L=9.85 mm as a standard;from 6 to 10 years, the sensitivity and specificity for the judgment of lymph node swelling were 95.59%and 100.00%, respectively when using L=10.25 mm as a standard;from 11 to 15 years, the sensitivity and specificity for the judgment of lymph node swelling were 92.31%and 100.00%, respectively when using S=4.40 mm as a standard. Conclusion High-frequency ultrasound is able to display the location distribution and morphological characteristics of the mesenteric lymph nodes in children, and also to accurately measure the diameters and flow signal distribution of the lymph nodes, thus will provide valuable evidence for the diagnosis of pediatric mesenteric lymphadenitis.