We report here for the first time the molecular characterization of a hyaluronidase from an aquatic source. SFHYA1 is the hyaluronidase found in the venom gland of stonefish, Synanceja horrida. Using a cDNA segment amplified with degenerate oligonucleotides based on the amino acid sequences of a conserved region in testicular-type hyaluronidases and a tryptic fragment of SFHYA1, clones encoding the precursor of this enzyme were isolated from a cDNA library prepared from stonefish venom glands. The deduced amino acid sequence of SFHYA1 shows that SFHYA1 is expressed as a precursor peptide with a 28-residue signal peptide for targeting it into endoplasmic reticulum. Mature SFHYA1 is a polypeptide composed of 449 residues containing three potential N-glycosylation sites, four putative hyaluronan-binding motifs [B(X)7B] and various residues implicated in substrate binding and catalysis. This cDNA was expressed in an active form in insect-cells but not in E. coli. Homology-based computational analyses suggested that SFHYA1 closely resembles the PH-20 family of hyaluronidases.