Onion extract was prepared by extracting onion with water, and the effects of the extract on pear polyphenol oxidase and browning of pear were investigated. The polyphenol oxidase of pear was inhibited by onion extract, and the inhibitory effect of onion extract toward pear polyphenol oxidase was increased with the heated extract. The inhibitory effect of the extract was increased with increasing heating temperature and time. The browning of pear juice was retarded by addition of both fresh and heated onion extracts. The onion extract inhibited the pear polyphenol oxidase non-competitively. Therefore, the inhibitory effect of onion extract against pear browning seems to be due to the inhibitory effect of onion extract against pear polyphenol oxidase.