The Nicobar treeshrew Tupaia nicobarica is an endemic mammal restricted in its distribution to Great and Little Nicobar islands in the Andaman Sea. This article aims to report basic information on the ecology and behaviour as well as a preliminary population assessment of this species on Great Nicobar Island. Nicobar treeshrews spend more than 60% of the day foraging, followed by resting or sleeping (12%). The proportion of time spent on major activities was significantly different across different time periods, with much of the feeding activity in the mornings and evenings. Nicobar treeshrews were observed largely solitarily or as breeding pairs. Observations on mating, aggression and vocalisation are also reported. Most of the ecological and behavioural traits are shared with one or more species of Tupaia in the region. Observations on this species point to its extreme arboreality in comparison to other Tupaia. The species also exhibited a high degree of insectivory during the study period. A combination of these two traits makes this species one among a handful of nonvolant foliage gleaning insectivorous small mammals that exist in the world today. The species was observed in moderate numbers both in the littoral forests as well as in the rainforests in the interior of the island. Although formally classified as endangered (on account of its restricted range), the species is common locally. The current status of the species seems to be stable in the Great Nicobar Island which has some of the best preserved forests in India.