Abstract: We isolated and sequenced a 480 bp cDNA encoding mature bovine interleukin-18 (bIL-18) from alveolar macrophages and splenocytes activated with LPS by RT-PCR. The bIL-18 gene was cloned into pET32a (+) vectors and sequenced. Nucleotide sequence of bIL-18 shares high homology with cattle. Fusional expression with pET32a (+) of bIL-18 of about 38ku was obtained by SDS-PAGE analysis after induction by IPTG in the E.coli BL21 expression system. The recombinant protein can augment T cell proliferation ConA-stimulated and IFN-γ production by MDBK. The IL-18 mRNA was constitutively detected in bovine alveolar macrophages with or without LPS, While, enhanced expression was detected in splenocytes and liver cells if treated by LPS, and can be weakly detected in peripheral blood mononuclear cells (PBMCs) treated by activators. Significant deference of IL-18 mRNA level may reflect the capacity to produce mature IL-18 in such tissues.