The study investigates the structure of sheep migration, socia-economic determinants of sheep migration as well as the cost and return of migrant and non-migrant sheep flocks in semi-arid zone of Rajasthan. The share of temporary sheep migration in the total migrant population is increasing, with declining rainfall, roughly at the rate of 1% per cm decline in rainfall. While the temporary migration was to the tune of 22%, the average size of migratory and non-migratory flocks was 79 and 48, respectively. Logit analysis indicated that the flock size, caste and technology adoption index were significant in determining the migration decision. The net return per sheep was higher for the non-migrant flock (Rs. 468)compared to the migrant flock (Rs.430).The paper concludes that although the non-migrant flocks have yielded more, migration could be considered an essential mechanism to save large animal flocks from fodder scarcity. Key words: Sheep, migration, structure, determinants, Rajasthan, semi-arid.