A method of preparing a superabsorbent polymer, the method comprising: forming a water-containing gel polymer by performing crosslinking polymerization of water-soluble ethylenically unsaturated monomers having acidic groups, of which at least part is neutralized, in the presence of an internal crosslinking agent including a compound represented by the following Chemical Formula 1, an encapsulated foaming agent, and a polymerization initiator; forming a base polymer in the form of powder by drying and pulverizing the water-containing gel polymer; and performing heat-treatment of the base polymer, wherein the heat-treatment is performed at a temperature of 150 °C or higher and 200 °C or lower for 20 min to 60 min, wherein the encapsulated foaming agent is used in an amount of 0.1 part by weight to 0.4 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer, wherein the encapsulated foaming agent has a core-shell structure, in which a core contains a hydrocarbon and a shell composed of a thermoplastic resin is formed on the core, wherein the encapsulated foaming agent has a mean diameter of 5 μm to 30 μm before expansion and a maximum expansion ratio of 5 times to 15 times in air, wherein the mean diameter is measured as a mean Feret diameter by an optical microscope, and wherein the prepared super absorbent polymer has a centrifuge retention capacity of 44 g/g to 54 g/g, as measured according to EDANA method WSP 241.3: in Chemical Formula 1, R 1 is a divalent organic group derived from alkane having 1 to 10 carbon atoms, and R 2 is hydrogen or a methyl group. forming a water-containing gel polymer by performing crosslinking polymerization of water-soluble ethylenically unsaturated monomers having acidic groups, of which at least part is neutralized, in the presence of an internal crosslinking agent including a compound represented by the following Chemical Formula 1, an encapsulated foaming agent, and a polymerization initiator; forming a base polymer in the form of powder by drying and pulverizing the water-containing gel polymer; and performing heat-treatment of the base polymer, wherein the heat-treatment is performed at a temperature of 150 °C or higher and 200 °C or lower for 20 min to 60 min, wherein the encapsulated foaming agent is used in an amount of 0.1 part by weight to 0.4 parts by weight with respect to 100 parts by weight of the water-soluble ethylenically unsaturated monomer, wherein the encapsulated foaming agent has a core-shell structure, in which a core contains a hydrocarbon and a shell composed of a thermoplastic resin is formed on the core, wherein the encapsulated foaming agent has a mean diameter of 5 μm to 30 μm before expansion and a maximum expansion ratio of 5 times to 15 times in air, wherein the mean diameter is measured as a mean Feret diameter by an optical microscope, and wherein the prepared super absorbent polymer has a centrifuge retention capacity of 44 g/g to 54 g/g, as measured according to EDANA method WSP 241.3: in Chemical Formula 1, R 1 is a divalent organic group derived from alkane having 1 to 10 carbon atoms, and R 2 is hydrogen or a methyl group.