Resistance of ticks to acaricides had spread dramatically in recent years, so changing of acaricides periodically is needed to avoid resistant strains. Cypermethrine is a new pyrethroid acaricide recently introduced in the skin parasites control programs in Egypt. Fourteen crossbred cows (Friesian X Egyptian native) were used to assess the acaricidal efficacy of cypermethrine against Boophilus annulatus ticks. Cows were allocated into treated and control groups, each consists of 7 animals. At day 0 before treatment, ticks of more than 4.5 mm in length attached to both treated and control animals were counted and every week thereafter. The average tick number on vaccinated and control animals were counted and the efficacy percentage of cypermethrine was then determined. The number of ticks which laid eggs were counted in treated and control animals and hatching percentage of eggs were then calculated. Spraying of animals with cypermethrine showed that complete elimination of ticks occurred early on the 7th day post-treatment. The average number of ticks was 1673 and that of controls was 1578 at day 0 before treatment. The maximum efficacy (100%) was sustained for up to 7 weeks post-treatment after which the efficacy was slightly dropped and reached 98%. The results of cypermethrine on oviposition and egg hatchability of the ticks which survived treatment were surprising. The percentage of ticks collected from treated cows that succeeded to lay eggs was 22%, the average number of eggs laid per tick was 259 and hatching rate was 8.6%.