Rhipicephalus (Boophilus) microplusis a tick that parasites mainly cattle and serve as vector to many diseases including babesiosis and anaplasmosis that are transmitted during hematophagous feeding, bringing economic losses due to animal sickness and decrease in production. The arising of resistance to substances used for chemical control, along with the risk of environmental and food contamination by these chemicals, has raised interest in biological control for ticks. Engorged females of R. microplus were collected from naturally infested animals and divided into three treatment groups, which were bathed in solutions containing 5000, 10000 and 15000 chlamydospores, and one treatment group. The present study aimed to evaluate the in vitro effect of the nematophagous fungus Pochonia chlamydosporia on R. microplus engorged females. It was observed that P. chlamydosporia (VC4) was able to infect R. microplus ticks at concentrations of 5000, 10000 and 15000 chlamydospores, having statistical difference (p<0.05) between all treatment groups when compared to the control group but not when compared among themselves. These results suggest the possibility of VC4 to be used as a biological control for R. microplus ticks.