The Upeneus oligospilus has a moderately elongated and slightly compressed body with a lengthy snout and a relatively small, slightly positioned downward mouth. It features long barbels on its chin and two distinct dorsal fins spaced apart. The coloration of its head and body is a mix of brownish to greenish grey on the upper side, adorned with reddish-brown flecks. The lower side transitions to white and is covered with small reddish-brown spots. A dark reddish-brown to black stripe runs along the side of the body from the snout's tip to the base of the caudal fin. The fish's fins are marked with dark reddish-brown or black stripes, bars, or patches, while its barbels are yellow or pale brown.