Abstract: 【Aim】 To determine the ultrastructural characteristics for diagnosis of dominant Dermacentor species, tick-borne vectors, in Xinjiang, northwestern China. 【Methods】 The ultrastructure and morphology of four dominant Dermacentor species, i.e.D. niveus, D. silvarum, D. nuttalli and D. marginatus, were observed by scanning electronic microscope on the basis of observation and indentification with stereo microscope. 【Results】 Differences existed in the idiosomal size and the enamel color of scutum among the four species. There are three odontoid processes on the ventral podomer Ⅳ (femur, tibia and metatarsus) of D. niveus and D. marginatus, and the odontoid processes are present on both tibia and metatarsus of D. nuttalli, but only present on the metatarsus of D. silvarum. Notable differences were also found in the seta arrangement of ventral palpus’s medial margin, the length of claws, and the claw-pulvillus length ratios of the four dominant Dermacentor species. 【Conclusion】 The number and location of the odontoid processes on ventral podomer Ⅳ and the morphology of spiracular plate are diagnostic characteristics for the four Dermacentor species, and a rapid species identification could be made by combining these characteristics with the seta arrangement of ventral palpus, the claw length and the claw-pulvillus length ratio.

Key words: Dermacentor, dominant species, ultrastructure, morphology, scanning electronic microscope, Xinjiang