The present invention relates to an organotin compound represented by R 1 O-Sn-OR 2 (where R 1 and R 2 are independently a primary, secondary, or tertiary alkyl group having 5 to 30 carbon atoms), a preparation method thereof, and a preparation method for polylactide using the organotin compound. The organotin compound of the present invention is easy to prepare and is used to prepare a polylactide resin having a high molecular weight at a high yield without using a separate initiator.