When fully grown oocytes are removed from their follicles, they can resume meiosis and mature spontaneously under in vitro conditions. However, nuclear maturation under in vitro condition is not accompanied by complete cytoplasmic maturation, which is essential for successful fertilization and the initiation of zygotic development. This study analyzed change of proteins in follicular fluids during the porcine follicular development. Follicular fluids were collected from follicles of diameter 1~2 mm, 2~6 mm and 6~10 mm in ovary of slaughtered pigs. Total proteins were extracted from follicular fluids by M-PER Mammalian Protein Extraction Reagent. We confirmed totally 27 same spots, 1 spot from follicle fluid of 2~6 mm follicle and 5 spots from follicle fluid of 6~10 mm in diameter were analyzed by MALDI mass spectrometry and searched on NCBInr. In results, spot No. 28 from 2~6 mm follicle was Ig lambda chain C region, and spot No.32 and 33 from 6~10 mm was Apolipoprotein A-(APOA4). Spot No.29 and 31 were failed to analyze. These results indicate that the porcine oocyte during in vitro maturation depend on specific different expressed proteins may play an important roles in the sequence of molecular events in porcine oocyte maturation and follicular development.