Abstract: The present article deals with the nest architecture, frequency distribution of head width and daily rhythm of out-and-in activities of the carpenter ant Camponotus tonkinus Santschi. It is found that this species constructs a very complicated ground nestconsisting of many passages and chambers. The queen chamber is usually located undermost in the nest. The head widths of workers range from 1.05 to 3.85 mm, and its frequency distribution is asymmetric monomodal with a peak at 1.4-2.0 mm (accounts for 72.7% of the total workers). In a sunny day, a typical daily cycle is bimodal, commence foraging in early morning, decline in midday and rise again in late aftemoon through dusk.

Key words: Camponotus tonkinus Santschi, nest architecture, frequency distribution of head width, daily outside activity rhythm.