The mir-155 family is not only involved in a diversity of cancers, but also as a regulator of the immune system.However, the evolutionary history of this family is still unclear. The present study indicates that mir-155 evolvedindependently with lineage-specific gain of miRNAs. In addition, arm switching has occurred in the mir-155family, and alternative splicing could produce two different lengths of ancestral sequences, implying the alternativesplicing can also drive evolution for intragenic miRNAs. Here we screened validated target genes and immunityrelatedproteins, followed by analyzation of the mir-155 family function by high-throughput methods like thegene ontology (GO) and Kyoto Eneyclopedin of Genes and Genemes (KEGG) pathway enrichment analysis.The high-throughput analysis showed that the CCND1 and EGFR genes were outstanding in being significantlyenriched, and the target genes cebpb and VCAM1 and the protein SMAD2 were also vital in mir-155-relatedimmune reponse activities. Therefore, we conclude that the mir-155 family is highly conserved in evolution,and CCND1 and EGFR genes might be potential targets of mir-155 with regard to progress of cancers, whilethe cebpb and VCAM1 genes and the protein SMAD2 might be key factors in the mir-155 regulated immuneactivities.