Novel cyclic organic silicon compounds of formula (1) can be synthesized in high yields and high purity by reacting a dichlorosilane of formula (3) with a cyclotrisiloxane of formula (4) in an aprotic polar solvent to form an .alpha.,.omega.-dichlorosiloxane of formula (2), and reacting the .alpha.,.omega.-dichlorosiloxane with an alkali metal according to the following reaction scheme. ##STR1##