A new species of Leptostraca, Nebalia cambodiana sp. nov. (Crustacea: Malacostraca), is described from Cambodia. The specimen was collected by light traps on a diving deck where the bottom consisted of fine sand and gravel. The new species is distinguished from all other known species of Nebalia by the following characteristics: rostrum very long, length nearly 3.5 times width; a compound eye with one distinct dorsal papilla and four small lobes on distal margin; an antennular flagellum with nine articles; the fourth article of the antennular peduncle with only one distal thick seta; the antennular scale is elliptical, with a length that is 2 times the width; exopod of the second maxilla is the same length as first article of its endopod; pleonites 5 to 7 with rounded denticles along their posterior dorsal margins; the protopod of pleopod 4 lacks serration along the posterior margin; and anal plates with distinct lateral ‘shoulder’.

The new species is the first species of Leptostraca found in South-east Asia. In this paper, we provide illustrations and a detailed description of the diagnostic characteristics of N. cambodiana sp. nov.