DnaK is a major heat shock protein and known to be highly conserved in all species. Previously, the dnaK in Streptococcus pneumoniae was cloned and the immunogenic nature characterized. In this study, dnaK mutants were generated by insertion of duplication mutagenesis and their characteristics examined. They had defective growths at all temperatures ($20^{circ}C-42^{circ}C$)and cell divisions, and formed filaments after a temperature shift from 30 to 42. A unique feature of the dnaK mutants of S. pneumoniae, unlike those of E. coli and B. subtilis, was the growth capability at high temperature ($42^{circ}C$) without producing the putative GroEL. Our results suggest that DnaK may serve as a regulator and/or modifier in GroEL gene expression.