Many fishes are capable of producing sounds for communication. Sound characteristics and sound production system of marbled rockfish Sebasticus marmoratus were investigated. The sound production system consists of swimbladder and swimbladder muscles. The muscles originate on the base of the pterotic bones of skull, pass the I VII ribs, then attach on the posterior portion of the swimbladder dorsolaterally. During dyadic agonistic encounters, the fish produce the sounds that consist of a series of individual pulses with average duration of (32.6±2.6) ms, average interpulse intervals of (51.8±81.4) ms, and dominant frequency of 68-175 Hz from fish about 13 cm in body length. The dominant frequency is consistent with the reciprocal of second energy cycle of pulse. The results suggested that the sound was produced by the contracting and relaxation of swimbladder muscles.