The defender against cell death 1 (DAD1) is a regulatory protein to inhibit the apoptosis process. The full-length cDNA of Haliotis diversicolor DAD1 (HdDAD1) was cloned by RACE according to DAD1 partial sequence of transcriptome. HdDAD1 was 553 bp, with a 339 bp open reading frame encoding a protein of 112 aa (HdDAD1). HdDAD1 contains a conserved DAD domain, with 3 transmembrane spans. Quantitative real-time PCR results indicated that HdDAD1 could be detected in all examined tissues, with the highest expression level in digestive tract, gill, hemocyte, mucus gland and kidney. There was also expression of HdDAD1 in different developmental stages. HdDAD1 expression level of larva stages was the highest, that of gastrula stage was middle, that of other stages was the lowest. HdDAD1 could respond bacterial challenge/thermal/hypoxia stress. There was significant up-regulation of HdDAD1 at 12 h after Vibrio parahaemolyticus challenge. HdDAD1 was significantly up-regulated, when water temperature rose from 25 to 28℃. The expression of HdDAD1 also significantly increased, when water temperature was 31℃ for 4 and 96 h. At 4 and 96 h post hypoxia stress, HdDAD1 significantly increased, too.