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The G-type lysozyme gene, non-specific immune molecule, was cloned from intestine of golden pompano (Trachinotus ovatus) by degenerate oligonucleotide primed PCR, including a complete open reading frame (ORF) of 804 bp. Homological protein analysis showed that the To-lysG in golden pompano shared a high degree of sequence identity with other known lysG sequences. In addition, tissue distribution analysis showed that To-lysG was expressed in nine tissues and had relatively high expression in spleen, head kidney and intestine. Then triplicate groups of golden pompano (18 cages) were fed twice daily to satiation with 0.0 (control), 0.25, 0.5, 1.0, 2.0 or 4.0 g kg−1 sodium butyrate (SB) diets for 8 weeks, respectively. Compared to the control group, 2.0 and 4.0 g kg−1 SB groups had higher lysozyme activities and the expression levels of To-lysG gene. After ammonia challenge, fish fed 1.0 g kg−1 SB group showed the highest survival rate (P < 0.05). Overall, these results suggest that the intestinal lysozyme activity and mRNA expression of T. ovatus were up-regulated significantly as dietary SB levels increased. These results indicated that To-lysG plays a crucial role in the regulation of intestinal immune function of dietary graded levels of SB in T. ovatus. Keywords: Trachinotus ovatus, Sodium butyrate, G-type lysozyme, Enzyme activity, Gene expression, Ammonia stress