Provided are a tumor proliferation inhibitor and a method for inhibiting tumor proliferation both of which can be applied to a minimally invasive cancer treatment using low-intensity pulsed ultrasound. The present invention provides a tumor proliferation inhibitor containing an ultrasound-sensitive substance and an acoustic cavitation phenomenon-enhancing substance, and provides a method for inhibiting tumor proliferation that can exhibit a tumor proliferation-inhibitory effect using the tumor proliferation inhibitor in combination with low-intensity pulsed ultrasound of a degree that is used in ultrasound diagnosis, and that can be applied to a minimally invasive cancer treatment using low-intensity pulsed ultrasound.