Bertya oblonga is a species of flowering plant in the family Euphorbiaceae and is endemic to New South Wales. It is a shrub with narrowly oblong to strap-like or sometimes linear leaves, separate male and female flowers, and oval to elliptic capsules with star-shaped hairs.
Bertya oblonga is a shrub that typically grows to a height of up to , its young branchlets densely covered with straw-coloured or greyish, star-shaped hairs. The leaves are narrowly oblong to strap-like or sometimes linear, long and wide with the edges flat or rolled downwards, the upper surface . Separate male and female flowers are borne on a peduncle long, the male flowers 30 to 45 stamens. Female flowers are on pedicels long, with narrowly triangular sepals long, hairy on the lower surface, and a densely hairy ovary. Flowering occurs from July to October, and the fruit is oval to elliptic, long with a single seed.
Bertya oblonga was first formally described in 1929 by William Faris Blakely in Proceedings of the Linnean Society of New South Wales from specimens he collected about , south-west of Molong in 1907.
This species of Bertya grows on rocky ridge tops or steep hillsides in shrubland, woodland or forest in scattered places between Boggabri, Molong and Denman.