The cave tick, Ornithodoros tholozani is the most important soft tick in central Asia and the Middle East. The populations of this species live in human buildings and animal shelters and are responsible for transmission of relapsing fever in different areas. Residual spraying of pesticides is a common control measure against this species, and vast regions of north west of Iran are sprayed annually with pyrethroids by the local residents. Application of limited range of acaricides and similarity in their mode of actions might contribute to emergenence of resistance, and decline of their efficacy. Thus, this research was conducted to identify the susceptibility level of different populations of this tick to some pesticides in old, well-known foci of relapsing fever. Populations of this tick were collected from animal shelters of Mahneshan, Khodabandeh, Tekab and Bijar districts in north west of Iran during 2012–2013. Adult ticks were exposed to different doses of permethrin, lambdacyhalothrin and carbaryl through topical and residual methods and mortality rate was measured after 24 hours. The bioassay revealed different levels of tolerance to permethrin in various populations of O. tholozani in the study area. The Bijar strain was susceptible and the LD₅₀ and LC₅₀ values for permethrin were 48.38 ng/tick and 96.98 µg/cm² respectively. Tekab, Khodabandeh and Mahneshan populations were resistant and resistance value in this group was 2. The Bijar strain was also susceptible to lambdacyhalothrin and LD₅₀ value for this compound was 8.37 ng/tick. In spite of the susceptibility to pyrethroids in Bijar strain, there was high resistance level to carbaryl and the LD₅₀ value was 5.45 mg/tick. Since different levels of resistance to permethrin were observed in various populations of O. tholozani, reviewing and refining the control measures against ticks, applying new formulations of acaricide mixtures and monitoring the susceptibility level of acaricides seem necessary in these regions. Moreover, future studies to identify the molecular characteristics of resistance to acaricides and determining the effective acaricide are highly recommended in these areas.