[Background] Mikania micrantha is an invasive alien plant with high invasiveness and perniciousness and severe impact on biodiversity and agriculture and forestry. To determine the level of invasiveness of M. micrantha in Hainan, monthly growth of the weed was measured to provide a baseline for the development of reasonable control. [Method] Monthly growth of M. micrantha was measured using a fixed point observation method over a 2-year period in 7 cities/counties of Hainan. [Result] M. micrantha could grow all the year round in Hainan. The average monthly growth of a shoot was 66 cm with an annual growth of 795 cm. M. micrantha grew the most in June (mean of 120 cm) and August (mean of 106 cm) and the least in January and December (mean of 21 cm). The fastest period of growth was from June to October with a mean of 489 cm or 61.5% of its yearly growth. Growth in April, May and November represented 24.7% of yearly growth (196 cm) and January to March and December, 13.8% of the yearly growth (or 110 cm). Flowering and fruiting occurred between October and March. Some populations flowered again from January to March while others from March to May. There was a highly significant positive correlation between growth of M. micrantha and temperature (R=0.91, p<0.01) and a significant positive correlation between growth of M. micrantha and rainfall (R=0.56, p<0.05). [Conclusion and significance] M. micrantha is a multi-branched plant and growth of a shoot reaches 795 cm yearly. Its growth allows it to establish populations rapidly. Both temperature and rainfall can affect M. micrantha growth.