The present disclosure provides methods for preparing a liposome composition. One of the methods includes the steps of: providing precursor liposomes encapsulating platinum-based precursors; and incubating the precursor liposomes with a salt solution to convert the platinum-based precursors to platinum-based drugs to form the liposome composition. The precursor liposomes are prepared by step of: hydrating the platinum-based drugs to form the platinum-based precursors; and adding the platinum-based precursors to a lipid bilayer vehicle to form the precursor liposomes. The liposome composition prepared by the methods shows improved encapsulation efficiency and enhanced drug loading capacity.