Soybean cyst nematode (SCN) disease is one of the most important diseases in soybean production.Calcium signal is involved in both the plant development and the resistance of disease.But it's not clear that the relationship between calmodulins and soybean-soybean cyst nematode interaction.This study used real time fluorescence quantitative PCR to study the relative expressions of SCaM1, SCaM2, SCaM3, SCaM4 and SCaM5 from susceptible cultivar Liaodou 15 and resistant cultivar ZDD2315 after SCN3 infecting.There were six time points, which were 1 day post inoculation (dpi), 3 dpi, 5 dpi, 9 dpi, 15 dpi, 20 dpi.Furthermore binary expression vector was constructed to research the subcellular localization of SCaM4 protein.The results stated that all five calmodulins changed in the six time points.The trend of the relative gene expressions of the five calmodulins after SCN infection was first increased and then decreasing.It reached the peak at the fifth day after infection among the six time points.And in resistant cultivar ZDD2315 the relative expression of SCaM4 was 12.73, in susceptible cultivar Liaodou15 the relative expression is as high as 6.48.The result of subcellular localization suggested that SCaM4 protein was located cytoplasm and cytomembrane.In summary calmodulins participate in the interaction of soybean and SCN3.Because SCaM1, SCaM2, SCaM3 are more similar and they are conserved, but the structures of SCaM4 and SCaM5 are different.So SCaM4 may be a special gene in the relationship of calcium signal and the interaction between soybean and SCN3.Next studying the function of SCaM4 in the process is necessary and important.