Little is known about the factors affecting pastoralists’ livestock vaccination decisions. In this paper, we use a novel survey-based dataset on pastoralists living in the Ruaha landscape in Tanzania, and employ several econometric approaches to identify the factors affecting pastoralists’ decision-making process about vaccination when disease occurrence and severity, vaccination and healthcare access costs and other related variables are known. Results from binary choice models that account for excess zeros indicate that socially and economically active households are more likely to vaccinate their livestock. The results also identify positive marginal effects of having wage earners and illness incidence on vaccination decisions. The results from mixture models also find that these same variables significantly lower the pastoralist’s probability to vaccinate no livestock. Most notably, vaccination cost significantly lowers the probability that pastoralists vaccinate any livestock, as well as the number of vaccinated livestock. These findings have important policy implications considering livestock health education, veterinary service infrastructure, and supply-side management.