A calmodulin-like protein (CaLP) that has been regarded as a Ca2+-dependent modulator protein in Escherichia coli L-form NC7 was purified by fluphenazine-sepharose 4B affinity chromatography. The molecular weight of the CaLP was approx. 18,000 kDa on SDS-Polyacrylamide gel electrophoresis and isoelectric point of 4.5 was confirmed by electric focusing gel (pH 3 to 10). The CaLP were heat stable and exhibited Ca2+-binding property. Further, the CaLP stimulated bovine hart phosphodiesterase activity. These results suggest the presence of Ca2+-regulatory system in prokaryotes.