Upon the termination of the United States Fish and Wildlife Service, Philippine Fishery Program in 1950, the bulk of the fishery collections was turned over to the Philippine Bureau of Fisheries. Some of the juvenile and postlarval marine fishes included in the plankton tows and night-light fishing collections were not worked out, except the young of tunas, which had been extensively studied. This paper presents a systematic study of young fishes which were collected by the biological staff of the research vessel Spencer F. Baird at Siokun Bay, Zamboanga del Sur, on November 19, 1948. The families of fishes represented in the Siokun Bay collection are Elopidae, Ophichthyidse, Synodontidae, Syngnathidae, Atherinidae, Mugilidae, Theraponidae, Ambassidae, Serranidae, Lutjanidae, Mullidae, Sillaginidae, Platycephalidaa, Pomacentridae, and Monacanthidae. The species of marine postlarval fishes described under the above families are as follows: Megalops cyprinoides, Ophichthys sp., Saurida tumbil, Ichthyocampus sp., Atherina sp., Mugil spM Ambassis sp., Therapon theraps, Epinephelus morrlma, Lut- ianus monostigma, Sillago sihama, Pseudupeneus sp., Platy- cephalus sp., Pomacentrus philippinus, Monacanthus sp., and Cantherines sp.