[Objective] Aim to study the effect of secretory aminopeptidase in Bacillus subtilis 168 on the growth, a gene knock-out mutant BS-AP-K was constructed. [Methods] Based on the Xer/dif recombinant system, the ywaD gene was deleted from the genome. The growth of wild type and BS-AP-K in different media was monitored. [Results] It turned out that the deletion of secretory aminopeptidase had a negative effect on the growth of the strain. The impaired growth rate of BS-AP-K strain can be overcome by amino acid supplements. [Conclusion] This study indicated that the secretory aminopeptidase played an important role in supplying amino acids required for growth by hydrolyzing proteins or peptides.