Animal dietary choices help understand a species’ feeding niche and are particularly relevant in conservation management. In this study, we aimed to gather knowledge on food niche and the foraging ecology of the Grizzled Giant Squirrel (Ratufa macroura) in Chinnar Wildlife Sanctuary, Southern Western Ghats, Kerala, India. Specifically, the objectives were to identify food composition, the seasonal variation in food choice and feeding technique. Through focal animal sampling, the Grizzled Giant Squirrel in Chinnar Wildlife Sanctuary was found to feed on 30 plant species belonging to 18 families. The most utilized plant family was Fabaceae, with eight species, followed by Moraceae (four species) and Anacardiaceae (two species). The feeding species included 22 trees, four climbers, one liana, one paraphyte, one shrub and one succulent species. The maximum duration of feeding was observed on Bauhinia racemosa (19.79%), followed by Tamarindus indica (14.08%) and Nothopegia beddomei (9.89%). The squirrel’s choice of diet was primarily affected by the availability of food tree species and food items rather than the season and non-tree species also have been reported from the diet of Grizzled Giant Squirrel. Even though the Grizzled Giant Squirrel shows plasticity in the food niche, the availability of mature trees and plants appears important for its conservation in the fragmented riparian forest in the Western Ghats, southern India.