Abstract: Amphioxus, a transitory form between the invertebrate and the vertebrate, is an ideal material for the study of animal evolution. The material used in this experiment is the common Amphioxus collected from Qingdao, Branchiosloma belcheri tsinytdoense Tchang et Koo.The purpose of this study is to find out the biochemical changes taking place in the metabolic processes of this animal and to demonstrate from the standpoint of molecular biology the speciality of its ontogenetic development. By means of ultracentrifugal technique and Oligo (dT)-cellulose affinity chromatography, ovarian Poly (A) RNA from Branchiostorna belcheri tsingtaoense Tehang et Koo was isolated and purified,The polysomes were obtained from the supernatant of the oocyte lysate through the ultracentrifugation of 1.0M sucrose solution and the total polysomal RNA was extracted from the polysome precipitate by phenol-chloroform-isoamyl alcohol (50:48:2). Poly (A) RNA. in the ovarian eggs of Amphioxus was purified by Oligo (dT)-cellulose chromatography to remove rRNA. Finally, Poly(A) RNA was precipitated by 2 volumes of ethanol and washed,with 4M LiCL and 3:1 ethanol saline to obtain Poly(A)RNA with biological activity. The recovery rate of the total polysomal RNA is 285μg per ml homogenate of the ovarian eggs.The mRNA-containing Poly(A),purified by means of Oligo(dT)-cellulose is 5.2% of the total polysomal RNA and 4% of the total RNA.The Polp (A)RNA obtained shows the typical absorption spectrum of RNA in ultraviolet spectral analysis.