This paper's focal point traces the establishment and growth of Taiwan's forest reserves (保安林，pronounced as hoanrin in Japanese and pao-an-lin in Chinese) during the Japanese colonial period. The first forest reserve was set up in 1900 with an area of 26.07 chia 甲 (1 chia is approximately 0.97 hectares) in a village around Erhlin二林. In 1942 there were 373,694 chia of forest reserves that accounted for 15 percent of Taiwan's total area of woodlands and forests. Analyzing the available statistics, we find that the growth of forest reserves appeared in different patterns with 1927-1928 as a turning point. The growth rate was higher in the first phase than in the second, however, the growth momentum appeared to decrease in the first phase while increasing in the second. This paper concludes that although the office in charge of forest affairs did change hands several times, the succeeding offices carried on most of the policies. Moreover, new programs were added up until 1942. These policies reflected that the colonial authority not only paid attention to the investigation and management of forests and woodlands as well as the disposition of forest products, but also made many efforts to do research and experiment. More important, the colonial authority initiated the establishment of forest reserves in Taiwan where natural geographical conditions made such a measure indispensable for territory security and public benefit. As the areas of forest reserves recovered to the pre-war level shortly after the war, it certainly can be considered as a legacy from the colonial period.