Rhipicephalus microplus ticks are one of the major causes of economic losses for livestock farmers, with significant economical losses, compromising the production chain. The inappropriate use of synthetic acaricides to control ticks contribute to the selection of resistance in different populations. Accordingly, the study of an alternative methods for tick control, including the use of entomopathogenic fungi, has gained attention. From these perspectives, the present study aimed to evaluate the compatibility of different Metarhizium spp. propagules with synthetic acaricides (amitraz, deltamethrin and the combination of cypermethrin, chlorpyrifos and citronellal) for 1, 5, 10 and 24h. The in vitro effect of deltamethrin and amitraz associated with fungal propagules in the control of a population of R. microplus females was also evaluated. Metarhizium spp. conidia and microsclerotia exhibited higher relative cultureability compared to blastospores after incubation with synthetic acaricides. The treatment of deltamethrin in association with entomopathogenic fungi promoted greater tick control than the fungus or synthetic acaricide alone, the association of deltamethrin with M. pingshaense resulted in greater tick control. The tick population used in the present study was less susceptible to deltamethrin, but not to amitraz, making it impossible to assess, with this tick population, whether there is any synergistic effect when amitraz is combined with entomopathogenic fungi for the control of R. microplus. Based on our results, it is not recommended that the tested acaricides be prepared/incubated with Metarhizium spp. blastospores before application.