Abstract: Nauplii Artemia urmiana was enriched with Thepax - a commercial product containing yeast cells of Saccharomyces cerevisiae. The Thepax-induced changes in biochemical parameters such as crude protein, fat, fiber, ash and energy were determined in the nauplii enriched at different times (6, 12 and 18 h) after hatching. To identify these changes, each group of nauplii (6, 12 and 18 h post-hatching) was enriched with 107 colony forming units (cfu mL-1) for a 24 h period. Enrichment with Thepax increased the ash content but decreased crude fat, protein and energy contents of Artemia urmiana nauplii (p<0.05). Thepax had no effects on crude fiber (p>0.05). As shown by the results of this study, it seems that probiotic enrichment with Thapax is favorable to improve the mineral (ash) content of Artemia urmiana nauplii. However, supplemented yeast probiotic with lipid emulsion and proteolytic enzymes is suggested for the nauplii enrichment.