To obtain the expression of Isoleucine Zipper modified soluble CD40L (IZ-sCD40L) in Pichia pastoris, firstly, DNA fragment of IZ-sCD40L was obtained by PCR and over-lap PCR . Then the expression vector pPICZaA-IZ-sCD40L was constructed. Nucleotide sequencing analysis indicated that the DNA fragment of IZ-sCD40L was correctly inserted into the pPICZaA vector. Linearized pPICZ(alpha)A-IZ-sCD40L was introduced into Pichia pastoris GS115. Positive clone was selected by PCR and its phenotype was determined. The positive clone was introduced with methanol. The results of SDS-PAGE and Western blot showed that product was recombinant Isoleucine Zipper modified soluble CD40L fusion protein.