The secretory efficiency of recombinant xylanase xynB from yeast Pichia pastoris between the ${alpha}$-factor preprosequence and a classical mammalian signal peptide derived from bovine ${eta}$-casein was compared. The results showed that although the bovine ${eta}$-casein signal peptide could direct high-level secretion of recombinant xylanase, it was relatively less efficient than the ${alpha}$-factor preprosequence. In contrast, the bovine ${eta}$-casein signal peptide caused remarkably more recombinant xylanase trapped intracellularly. Real-time RT-PCR analysis indicated that the difference in the secretory level between the two signal sequences was not due to the difference in the transcriptional efficiency.