A survey was conducted to study the effects of environmental factors on abundance of Anopheles minimus Theobald and its seasonal fluctuation in 5 locations in southern and eastern Taiwan for 1 yr. The 5 locations were Hualien, Taitung, Pingtung, Kaohsiung, and Tainan. Seasonal fluctuation was different for each of these 5 locations. Peaks were found in November and May, November, December, January, and March in Hualien, Taitung, Pingtung, Kaohsiung, and Tainan, respectively. The number of A. minimus larvae per dip was significantly correlated with total P, NH 4 -N, K + , Ca +2 , Mg +2 , and Mn +2 and significantly correlated with stream velocity and conductivity. Thus, the numbers of A. minimus larvae were expressed by the following equation: y = −0.161 + 0.150 * water velocity + 0.109 * conductivity + 0.302 * total P + 0.026 * NH 4 -N − 0.120 * K + + 0.023 * Ca +2 + 0.131 * Mg +2 + 0.140 * Mn +2 ( R2 = 0.50). In Taiwan, both the A and B forms of A. minimus were found in Tainan, Pingtung, Taitung, Hualien, and Kaohsiung.