Abstract: This paper revealed the population dynamics of Dactylogyrus on the gills of Leuciscus idus Linaeus by field investigation from April 2009 to July 2012 in Irtysh River. The results showed that three Dactylogyrus species infect L. idus including Dactylogyrus tuba, Dactylogyrus micracanthus and Dactylogyrus alatus, and their infection rate was 28.47% and mean infection intensity was 7.39 (142). The prevalence was varying among host body length (L) groups, as the infection rate was the highest (50%) in L30 cm, but the Dactylogyrus was zero in L10 cm. Dactylogyrus was in the aggregation distribution mode in different groups. The infection intensity showed no significant difference (P0.05) among different groups. Population of Dactylogyrus in host was aggregated distribution in different groups. A Dactylogyrus of L. idus Linnaeus was collected from the Irtysh River, Northwest China. The specimens were identified as Dactylogyrus alatus f. major Linsyow (1878) according to morphological characteristics, and represent the first record in China. The main morphological characteristics were described and drawn, and also compared to those from the gills of other species of L. idus in China.