The objective of this study was to evaluate the larvicidal potential of a crude ethanol extract (CEE) of soapberry Sapindus saponaria stem peel on the cattle tick Boophilus microplus. Tick larvae obtained by incubating engorged females, collected from naturally infested cattle, were placed in envelopes of filter paper impregnated with different concentrations of CEE in the test group, and distilled water in the control group. Four repetitions were made with each solution (n>120). Mortality was observed after 48 hours. Lethal concentration values of 1,258 ppm (LC50) and 6,360 ppm (LC99) were obtained.Este trabalho objetivou avaliar o potencial larvicida do extrato bruto etanólico (EBE), da casca do caule de Sapindus saponaria, sobre Boophilus microplus. Larvas desse carrapato foram obtidas pela incubação de teleóginas, coletadas de bovinos naturalmente infestados. As larvas foram acondicionadas em envelopes de papel-filtro, impregnados com diferentes concentrações do EBE no grupo teste, e com água destilada no grupo controle. Quatro repetições foram feitas com cada solução (n>120). A mortalidade foi observada após 48 horas. Foram obtidas concentrações letais CL50 de 1.258 ppm e CL99 de 6.360 ppm.