A inertial rocking type exercising device includes a rotation main body, and a support rack. The rotation main body is provided with two semi-spherical bodies, and a rotation disk rotatably mounted on the two semi-spherical bodies. The rotation disk is provided with an extension portion for receiving a counterweight ball. The support rack is provided with two handles and has a first end inserted into one of the two semi-spherical bodies, and a second end provided with an arcuate catch plate. Thus, the inertial rocking type exercising device that has a small volume and can be assembled and dismantled easily and conveniently.