The study of the relation between population dynamics and habitat factors of Hynobius formosanus was conducted in the Alishan and Zijhong areas from January 1990 to April 1991. Sample areas were set up in appropriate habitat selected along the New Central Cross-island Highway. Results from using the mark-recapture method indicated that the Alishan plots had the largest population of Hynobius formosanus (129 individual counts), B plot in Zijhong had the second largest population (52 individual counts), and the Shenmu Forest Road plot had the least. Spring was the peak season to encounter Hynobius formosanus. In the winter less Hynobius formosanus were captured, perhaps due to the lower temperature, drier surface layer, and breeding migration. The highest number of capture per unit area (per 100 m2) was in the Zijhong area (6.35 individuals). The Lulin plot had lower number of capture per unit area (1.08 individuals) due to over concentration. Population composition analysis showed that the juvenile Hynobius formosanus smaller than 17 mm appeared in great number in spring, which indicated that the breeding season of the species starts in September and continues to January of the next year in the Alishan area. The breeding season in the Tataka area is slightly delayed.