This study establishes the determinants of household vulnerability to food insecurity in pastoral households of Kajiado and agropastoral households of Makueni Counties of Kenya. A randomly selected sample of 198 households was interviewed. Descriptive analysis showed that pastoral households of Kajiado County were more vulnerable to food insecurity (VFI) with a VFI of 0.59 than agropastoral households in Makueni County, who had a VFI of 0.27. Further, a two stage least squares approach established that vulnerability of households to food insecurity is determined by land size, household size, rainfall and herd size for Makueni County and access to climate information, herd size, off-farm employment and gender of the household head for Kajiado County. The findings imply that Makueni County needs access to and control over land resources, destocking through improved livestock breeds and creation of a microclimate to enhance rainfall levels. For Kajiado County, policies need to promote access to climate information, diversification of livelihoods and female access to production resources.