Major histocompatibility complex (MHC) is a highly polymorphic gene family in the vertebrate genome, and its coding products play an important role in the vertebrate immune system. Most of the world's surviving crane (Gruidae) species are threatened due to habitat pollution and destruction. To understand the information of MHC-I sequences of cranes, universal primers were designed to isolate and clone MHC-I sequences from genomic DNA extractions from blood of a common crane (Grus grus) and a wattled crane (Bugeranus carunculatus) in captivity. Two and three sequences of 1 500 bp were isolated respectively from the genomes of G. grus and B. carunculatus, suggesting the existence of at least two MHC-I loci in cranes. All nucleotide sequences could be translated into normal amino acid sequences, indicating that they might execute certain functions (Fig. 1). The mutation rates of nucleotide and amino acid in the antigen binding region were 5.0%, 9.6% for G. grus and 9.1%, 14.6% for B. carunculatus, respectively (Table 2). The antigen binding sites were subject to strong positive selection, as the values of dN/dS were 7.348 8 and 2.145 2 for G. grus and B. carunculatus, respectively (Table 3). Bayesian trees showed that MHC-I sequences did not cluster according to crane species, indicating trans-species polymorphism of MHC-I genes in cranes (Fig. 2). The universal primers and sequences of MHC-I genes obtained here could lay a foundation for further study of conservation genetics of endangered cranes in the future.