This disclosure relates to a method for preparing organic microbubble complex particles including sonicating an aqueous solution including a graphene compound and an amphiphilic material in the presence of a gas, a method for preparing organic microbubble complex particles including injecting an aqueous solution including a graphene compound and an amphiphilic material into a microchannel, and an organic microbubble complex particle including a core part including at least one gas selected from the group consisting of an inert gas and carbon dioxide, and a shell layer including a graphene compound and an amphiphilic material, and an ultrasound contrast agent including the organic microbubble complex particles.