A preparation method of a polysiloxane-polylactide block copolymer, comprising the step of ring-opening polymerization of lactide monomers in the presence of a polysiloxane compound of the following Chemical Formula 3, wherein the ring-opening polymerization of lactide monomers is performed in the presence of an organic metal complex catalyst of the following Chemical Formula 4 or in the presence of catalysts including both compounds of the following Chemical Formula 5 and 6: wherein m is an integer of 5 to 150, R 1 and R 2 are the same as or different from each other, and are each independently substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 carbon atoms, or substituted or unsubstituted aryl having 6 to 10 carbon atoms, and X and Y are each independently an alkoxy group having 1 to 12 carbon atoms or a hydroxyl group; wherein n is an integer of 0 to 15; p is an integer of 0 to 2; a is 0 or 1; M is Sn or Zn; R 3 and R 5 are the same as or different from each other, and are each independently hydrogen, substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 carbon atoms, or substituted or unsubstituted aryl having 6 to 10 carbon atoms; R 4 is substituted or unsubstituted alkylene having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkylene having 3 to 10 carbon atoms, or substituted or unsubstituted arylene having 6 to 10 carbon atoms; and A 1 and A 2 are each independently an alkoxy group having 1 to 12 carbon atoms or a carboxyl group; wherein n is an integer of 0 to 15; R 3 and R 5 are the same as or different from each other, and are each independently hydrogen, substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 carbon atoms, or substituted or unsubstituted aryl having 6 to 10 carbon atoms; R 4 is substituted or unsubstituted alkylene having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkylene having 3 to 10 carbon atoms, or substituted or unsubstituted arylene having 6 to 10 carbon atoms; [Chemical Formula 6] MA 1 p A 2 2-p wherein M is Sn or Zn, p is an integer of 0 to 2, and A 1 and A 2 are each independently an alkoxy group having 1 to 12 carbon atoms or a carboxyl group. R 1 and R 2 are the same as or different from each other, and are each independently substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 carbon atoms, or substituted or unsubstituted aryl having 6 to 10 carbon atoms, and X and Y are each independently an alkoxy group having 1 to 12 carbon atoms or a hydroxyl group; wherein n is an integer of 0 to 15; R 3 and R 5 are the same as or different from each other, and are each independently hydrogen, substituted or unsubstituted alkyl having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkyl having 3 to 10 carbon atoms, or substituted or unsubstituted aryl having 6 to 10 carbon atoms; R 4 is substituted or unsubstituted alkylene having 3 to 10 carbon atoms, substituted or unsubstituted cycloalkylene having 3 to 10 carbon atoms, or substituted or unsubstituted arylene having 6 to 10 carbon atoms;