The hydrogel composition of the present invention includes an amphiphilic block polymer having a hydrophilic block chain having 20 or more sarcosine units and a hydrophobic block chain having 10 or more lactic acid units, and water as a dispersion medium. In the hydrogel composition, the amphiphilic block polymer is preferably present as hydrogel nano-particles having a particle diameter of 100 nm or less. The hydrogel can be prepared by mixing an amphiphilic block polymer with an aqueous liquid. The hydrogel is preferably substantially free of an organic solvent.
