Abstract: Protein phosphatase-2A (PP2A) is a major serine/threonine phosphatase and accounts for more than 50% serine/threonine phosphatase activity in eukaryotes. The holoenzyme of PP2A consists of the scaffold A subunit, the catalytic C subunit and the regulatory B subunit. The scaffold subunit, PP2A-A or PP2A-A, provides a platform for both C and B subunits to bind, thus playing a crucial role in providing specific PP2A activity. To explore the possible functions of PP2A in the development of lower vertebrates, we analyzed the differential mRNA and protein expression patterns of the scaffold subunit A for PP2A using RT-PCR and western blot analysis on 9 tissues and 12 developmental stages of goldfish and zebra fish embryos. Our study demonstrated the following results: (1) PP2A-A/ mRNAs were differentially expressed in various tissues of the goldfish and zebra fish; within the same tissues of the two types of fish, PP2A-A/ mRNAs had the different expression patterns. (2) PP2A-A/ proteins were differentially expressed in various tissues of the goldfish and zebra fish; within the same tissues of the two types of fish, PP2A-A/ subunits had the same protein expression pattern. (3) PP2A-A/ mRNAs abounded in the stages of two-cell, multiple-cell, blastula of goldfish and zebra fish embryos. Especially, PP2A-A mRNA had a distinct increase in the goldfish eye pigmentation stage embryo, suggesting it was essential to the formation of the goldfish eye pigmentation. (4) In the 12 developmental stages of embryos, PP2A-A/ proteins had the high expression level, suggesting that PP2A-A/ appeared to play a very important role during goldfish and zebra fish development. These results suggested that PP2A-A/ might play a very important role during embryos development and also in adult tissue homeostasis of gold fish and zebra fish.