Abstract Microcystin-LR (MCLR) is a widespread cyanotoxin produced in algal blooms, and has potent hepatotoxicity and tumor-promoting activity. We cloned the full-length cDNA of Id1 in bighead carp. The full-length Id1 cDNA was 954bp and contained a 387bp ORF. Bighead carp Id1 shared high identity with zebrafish Id1 amino acid sequence, and phylogenetic analysis showed that teleost Id1 evolved closely. Bighead carp Id1 constitutively expressed in all tested tissues in normal. When tested at two different time points post exposure and at 3 different MCLR doses, Id1 expression increased in a time-dependent pattern, and Id1 expression in brain was very sensitive to MCLR exposure. The present study will help us to understand more about the evolution of Id1 molecule and its role in the MCLR induced cell differentiation and cancer promoting in bighead carp.