Boiga barnesii is a species of cat snake endemic to Sri Lanka.

It is distributed in the lowlands and midlands up to approximately 600 m (2,000 ft) above sea level, with known localities include Matale, Kandy, Gannoruwa, Gampola, Ambagamuwa, Balangoda, Labugama and Sinharaja Rain Forest.

Barnes' cat snake is mainly a forest-dwelling species but may occasionally be found in human habitats.

It is the smallest cat snake in Sri Lanka and grows up to a maximum of about 600 mm (24 in) in snout-vent length.

The dorsum of B. barnesii is reddish-brown, with a purplish brown vertebral series of blotches running from nape to the mid-tail region.