Seroconversion in pregnant cattle and buffaloes as well as their calves following vaccination with inactivated RVF vaccine was estimated by the hae magglutination inhibition (HI), comple ment fixation (CF), serum neutralization (SN) and agar gel precipitation (AGP) tests. The AGPT gave a negative result with both species, while the other tests did not show any significant difference between the two species. A correlationship could be established between the HI, CF and SN tests, from which it is recommended to vaccinate calves of the two species at the age of 3 months.