Abstract: Artemia is a practical and suitable larvae food for both marine and fresh water crustaceans and fishes. Yeast probiotic enrichment of Artemia urmiana nauplii, found in Uromieh Lake of Iran, has not been documented in literature. The nauplii were enriched with Thepax, a commercial probiotic material containing yeast cells of Saccharomyces cerevisiae and the best time and concentration of the enrichment have been evaluated. To identify the optimal concentration of yeast cells, each group of nauplii (6-, 12- and 18-h after hatching) have been enriched with three treatments containing 104, 107 and 1010 colony forming units (CFU mL-1). In result, the maximum survival rate of nauplii was in concentration of 107 CFU mL-1 (p=<0.05). As the most yeast cells have been seen in the 6-h group (p=<0.05); the best time of enrichment was at 6 hours after hatching. In contrast to probiotic enrichment of other Artemia species, this study showed that the earlier enrichment of Artemia urmiana nauplii has better results.