An ultrasound-induced drug delivery system is described, using a drug carrier containing a plurality of nanobubbles and a high concentration of a drug in one microcapsule, and a method for preparing the drug delivery system, by generating the nanobubbles in an oil into which the drug is dissolved using a nanobubble generator, and then microencapsulating them. The drug delivery system has an effect of maximizing a drug delivery efficiency as the nanobubbles collapse or aggregate when the ultrasound is applied to the drug delivery system. Since the drug delivery system contains a plurality of nanobubbles within the microcapsules, it can also be used as a contrast agent, or can be used to simultaneously perform in vivo diagnosis and treatment.