[Background] In the recent two decades, Merremia boisiana grows rapidly and abnormally, causes death to trees and destroys biodiversity and forestry production severely in Hainan and Guangdong of China. To determine the level of invasiveness of M. boisiana in Hainan, monthly growth of the weed was measured to provide a baseline for the development of reasonable control. [Method] Monthly growth of M. boisiana was measured using a fixed point observation method over a one-year period in three study sites of three cities/counties of Hainan. [Result] M. boisiana could grow all year round in Hainan. Monthly growth of a new shoot averaged 134 cm and yearly growth, 1607 cm. M. boisiana's growth peaked in April (mean of 206 cm) and September (187 cm). The slowest growth of M. boisiana occurred in November with a mean of 86 cm. A new shoot of M. boisiana could grow by 1326 cm from January to September, representing 82.5% of the yearly growth, while October to December represented only 17.5% of the yearly growth or 281 cm. There were significant differences in growth among the three habitats, with values of 188 cm in Dingan, 131 cm in Baisha, and 83 cm in Wuzhishan. The seeds of M. boisiana could germinate from March to July and the periods of flowering and fruiting occurred from April to July. In those sites, mean monthly temperatures varied between 17 and 28℃ with mean monthly rainfall of 28~396 mm. There was no significant correlation between growth of M. boisiana and temperature or rainfall. [Conclusion and significance] M. boisiana grows and spreads rapidly and in great abundance in open habitat in Hainan. Monthly average growth can reach up to 188 cm and can be affected by habitat, altitude and existing vegetation.