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Abstract. Alpha-Zearalenol (α-ZEA) is one of derivatives from Zearalenone (ZEA) which impacts mammalian reproduction and development. Previous studies have shown that pigs are sensitive to the estradiol-like effects of α-ZEA. However, the effect of α-ZEA for the early embryonic development has not been fully studied. The objective of this study was to identify the direct toxicity of α-ZEA on porcine preimplantation embryonic development, embryo quality and expression of developmentally important genes. Presumptive zygotes were cultured in porcine zygote medium 3 (PZM-3) in the presence of α-ZEA (n=2,957) or 17β-estradiol (E2) (n=1,333) dissolved in 0.1% Dimethyl Sulfoxide (DMSO) from 24 to 84 h post insemination followed by determination of apoptotic cell numbers and transcript levels of BAX, BCL2L1 and POU5F1 in blastocysts. Cleavage rates on day 2 were significantly decreased in 10, 30 and 60 μM α-ZEA groups; whereas blastocyst rates on day 6 were significantly decreased in the 30 and 60 μM of α-ZEA groups. Only the 100 μM E2 group significantly decreased cleavage and blastocyst rates. Total cell numbers (TCN) in blastocysts were significantly lower in the 10 µM α-ZEA group, but no differences in apoptotic cell rates were found. The expression levels of POU5F1 and BCL2L1 transcripts were similar; however, levels of BAX transcripts and the BAX/BCL2L1 ratio were increased in both α-ZEA groups. Since α-ZEA and E2 did not elicit similar effects, results suggest that α-ZEA might impact porcine preimplantation embryonic development through pathways other than estrogen receptor binding. Key words: α-ZEA, Porcine, Embryonic development, Gene expression, Porcine (J. Reprod. Dev. 58: [338][339][340][341][342][343] 2012) M ammalian embryogenesis is a fascinating process that is essential for setting the stage for later development. Embryonic development is sensitive to environmental toxicants such as mycotoxins. There are more than 1,500 existing environmental mycotoxins such as Zearalenone (ZEA), which is a nonsteroidal estrogen. Zearalenone mimics the hormone estrogen and thereby affects early porcine embryonic development.Zearalenone was identified in 1952 and its chemical structure was determined in 1966 [1,2]. Zearalenone is produced by several Fusarium species found worldwide in corn, wheat, and other cereals stored improperly in wet conditions [3]. Alpha-ZEA has a higher estrogenic potency than ZEA and the other isomeric forms [4]. Alpha-ZEA might bind to estrogen receptors 1 and 2 to decrease fertility, increase embryolethal absorption, reduce litter size, and change the weight of the adrenal and pituitary glands [5]. ZEA and α-ZEA were detected in follicular fluid (FF) from the follicles ≥ 6 mm which may correlated with poor embryonic development [6]. However, the mechanism of α-ZEA toxicity, and its effect on porcine embryogenesis are poorly defined. There is a need for understanding how α-ZEA affects embryonic genome activation and developmental potential of porcine embryos.The objective of this study was t...