H9N2 avian influenza viruses (AIVs) are widely distributed in poultry and have attracted continued attention because of their high reassortment potential and ability to cross species barriers. In March 2019, two H9N2 viruses were isolated from a pig and a chicken, respectively, in Shandong Province, China. In this study, we characterized the whole-genome features, phylogenetic relationships, molecular characteristics, and pathogenicity of the two viruses in mice. Whole-genome sequence analysis showed that the eight gene segments of the two isolates shared 99.9%–100% nucleotide sequence identity. Phylogenetic analysis showed that the two viruses had the same reassortant genomic composition, with the HA and NA genes related to the Y280-like lineage, the PB2 and M genes related to the G1-like lineage, and the PB1, PA, NP, and NS genes related to the SH/F98-like lineage. According to the historical H9N2 genotype nomenclature, both viruses were classified as G57 and were genetically closely related to H9N2 viruses previously detected in environmental samples in Jiangsu Province, China. Several amino acid substitutions previously associated with mammalian adaptation, receptor binding, viral replication, and antigenic variation were identified in both isolates; however, their biological effects were not experimentally evaluated in this study. In mice, both viruses replicated in the lungs and nasal turbinates and caused interstitial pneumonia, but neither virus caused significant body weight loss or death, and no virus was detected in the liver, spleen, kidney, or brain. Overall, the two H9N2 viruses isolated from a pig and a chicken showed highly similar whole-genome characteristics and shared several molecular features previously associated with mammalian adaptation. However, given the limited number of isolates and the lack of direct epidemiological and transmission evidence, the present study does not provide sufficient evidence to establish direct poultry-to-swine transmission, the direction of transmission, or sustained cross-species transmission.