Batrachoididae, one of the most well-studied soniferous fishes, are typical examples of fish using intrinsic sonic muscles to excite vibration of swim bladder to emit sound. Most fishes possess a single swim bladder including the Batrachoididae. However, the grunting toadfish (Allenbatrachus grunniens) was found to have two separated swim bladders located in the dorsal part of the abdominal cavity; the size of the swim bladders were quite similar. Sonic muscles were firmly attached to the lateral side of each swim bladder. The aims of this study were to (1) investigate the specialized swimbladder morphology and the acoustic signals of the grunting toadfish (A. grunniens), (2) to falsify the hypothesis that this unique form of swim bladder is a synapomorphic character, and species that possess this character are sister groups. The vocal repertoire in grunting toadfish can generally divided into two types ¡V grunt and boatwhistle. Grunts were harmonic signals with shorter call duration, and could be emitted alone as single grunt (i.e., hand-held grunt) or in series (known as grunt train). Boatwhistles were also hamonic but much longer in call duration and usually appeared in succession. A small portion of signals were found to have acoustic beats, which was previously described in the three-spined toadfish (Batrachomoeus trispinosus), which also possess a pair of swim bladders. Therefore, signals with acoustic beats may be a key character for generating sound by two separated swim bladders. Comparing the morphological measurements of swim bladders indicated that there were no significant differences between swim bladders on different sides. However, comparisons between genders showed that the width, thickness, and weight of sonic muscle in females were significantly higher than males. Less wide sonic muscles with shorter sonic muscle fibers may enables the muscle to contract at a higher velocity in male fishes. However, females were found to have thicker sonic muscle, which indicated that the vocal ability in females may be higher than it was expected. The sonic muscle fibers of females have a larger myofibrillar region compared with males, which have a relatively larger central core. These characters may increase the fatigue-resistance of sonic muscle in males, which can contract at a relatively higher rate for a longer duration. Species with two separated swim bladders were found to be sister group in the molecular phylogenetic tree, implying that this specialized morphological character is synapomorphy.