cDNA cloning and 5′-RACE experiments were conducted on β-amyloid precursor protein (APP) using porcine ovary mRNA. The isolated cDNA clone and the clones generated by 5′RACE spanned 3,051 bp containing the complete open reading frame of APP which consisted of 770 amino acid residues. The amino acid sequence of porcine APP was 97.8, 97.1, and 97.4% homologous to those of human, mouse, and guinea pig APPs, respectively. The expression of APP in several porcine tissues was examined by Northern blot analysis. The ovaries and adrenal glands showed a strong expression of the APP mRNA, as did the granulosa cells from small and large follicles of the porcine ovary. RT-PCR analyses using two primer sets revealed that the porcine ovary expressed at least four types of APP mRNAs. Western blot analysis was conducted using the extract of granulosa cells and the fluid of ovarian follicles, and the results indicated that the follicular fluid contained soluble APP in relatively high content. These results suggest that APP undergoes proteolytic processing and/or degradation within the follicles during follicular development.