A 3-methylthiopropanal is produced by a method comprising the step of supplying an acrolein and a methyl mercaptan together or sequentially with an acidic compound and a basic compound into a reaction system to react the acrolein with the methyl mercaptan, wherein the basic compound is used in an amount of about 0.3 mol or less per mol of the acidic compound. In accordance with the present invention, a 3-methylthiopropanal with high quality is produced while suppressing the production of by-products having high boiling points.