The proteases such as alkaline protease, neutral protease, papain, bromelain, and complex protease were screened using the degree of hydrolysis (DH) and peptide yield (TCA-YSP) as indicators. The crude oligopeptide of cashew nut was isolated by ultrafiltration, Sephadex-G15, Sephadex-G50 and semi-preparative liquid chromatography. The purity and structure of cashew nut oligopeptide were identified through analytical liquid chromatography and infrared spectra. The results showed that DH and TCA-YSP were (17.06±1.52)% and (26.28±0.13)% respectively, which were significantly higher than those of other proteases. Therefore, alkaline protease was the most suitable protease. The sequence of cashew nut oligopeptide was Ile-Ile-Ala-Pro-Ala-Val-Ala-His (IIAIPAGVAH). The result of antiallergic effect of cashew nut oligopeptide showed cashew oligopeptide at 200 μg/mL significantly inhibited the release of histamine, the expression of β-aminohexose glycinase (β-HEX), and phosphatidylserine eversion in mast cell, indicating that cashew oligopeptide extracted from cashew nut owned outstanding antiallergic effect.