Activity pattern and food habits of Grizzled Giant Squirrel were investigated in Srivilliputhur Grizzled Giant Squirrel Wildlife Sanctuary from December 2011 to March 2012. Focal animal sampling method was used to record the activity pattern and food habits. Sampling was done in three different habitats viz., Private land, Reserve forest and Temple land. Feeding was the dominant activity accounting for 35.4% of the activity period. Bimodal feeding pattern was observed in Squirrels, the observations were made from early morning hours to till (0600-1800) late evening hours. The Squirrels feed upon 23 plant species; among them 11 were trees species, 10 climbers and 2 shrubs. Seven types of plant parts were used by Squirrels. Leaf consumption was high (38%) followed by fruit (24%). The high consumption of leaves was due to easy availability of leaves and limited availability of other plant parts. Squirrel‟s invasion into Private Land and Temple Land was observed which can be attributed to abundance and easy availability of food plants, canopy continuity and less predatory pressure.