Disclosed is an improved process for producing nitroisourea derivatives which is necessary for producing nitroguanidine derivatives having an insecticidal activity. Specifically disclosed is a process for producing nitroisourea derivatives represented by the following general formula (3), which is characterized in that nitroisourea derivatives represented by the following general formula (1) and amines represented by the following general formula (2) or a salt thereof are reacted in the presence of a catalytic amount of a hydrogen carbonate,