A new species of goby, Lubricogobius nanus, is described from near Alotau, Milne Bay Province, Papua New Guinea on the basis of four adult specimens, 9.5–10.9 mm SL. Diagnostic features include 10–11 segmented dorsal-fin rays, 8–9 segmented anal-fin rays, the presence of both anterior and posterior nostrils, a low fleshy keel mid-dorsally and mid-ventrally on the caudal peduncle, a mid-lateral row of widely-spaced sensory papillae on the side of the body, approximately 15 scattered sensory papillae on the middle portion of the caudal fin, body depth 3.2–3.4 in SL, mainly brown coloration with yellow fins, and an exceptionally small size (<11 mm SL). Photographs and comparative morphological data are presented for the other four members of the genus, including L. dinah, L. exiguus, L. ornatus, and L. tre.