In East and Southeast Asia, various phenological patterns are known in each forest, such as temperate forests, subtropical forests, seasonal tropical forests, tropical rain forests, and tropical montane forests. However, the phenology of tropical montane forests has been less extensive than that of tropical lowland forests. To systematically understand the diversity of phenological patterns in East and Southeast Asia, we conducted (1) the field observation of tree phenology in tropical montane forests in Bidoup-Nui Ba National Park, Central Highland of Vietnam, where phenology had not been previously studied, and (2) the statistical comparison of phenological patterns among the nine well-studied areas in Southeast Asia. For (1) the field observation, five plots were installed at the elevation range from 1460 m to 1920 m in the national park, and monitored leafing, flowering, and fruiting events of 17–19 dominant tree species in each plot (five individuals per species; in total 91 species consisted of four deciduous and 87 evergreen trees) for seven times; in June, September, and December 2018, April, July, and October 2019, and January 2020. As a result, leafing, flowering, and fruiting events were observed for 91 spp. (100.0 %), 65 spp. (71.4%), and 54 spp. (59.3 %), respectively. The number of leafing species ranged from 20 spp. (22.0%) in June to 91 spp. (100%) in April, which was significantly influenced by all of day length, precipitation, and temperature. On the other hand, the number of flowering species ranged from 15 spp. (16.5%) in September to 33 spp. (36.3%) in December, which was influenced by day length and precipitation. The number of fruiting species ranged from 12 spp. (13.2%) in January to 27 spp. (29.7%) in July, which was not significantly influenced by any of the meteorological factors. For (2) the statistical comparison of phenological patterns, we assembled the phenological data from previous studies in nine locations in East and Southeast Asia (2 temperate forests, 2 subtropical forests, 1 seasonal tropical forest, 2 tropical rain forests, and 2 tropical montane forests) and performed a cluster analysis for phenological patterns. As a result, the phenological pattern of Bidoup-Nui Ba National Park was similar to that of Mt. Kinabaru, though the two has different climatic patterns. This suggests the existence of other climatic factors that influence forest phenology. Based on the results of (1) and (2), we constructed a new hypothesis that showed the process of diversification of community phenology in correlation with local meteorological factors, though further observations are needed to assess the diversity of phenology in East and Southeast Asia.