A medical insertion mechanism is provided and includes a base, a needle holder slidably disposed on the base, a needle disposed on the needle holder, a cannula holder arranged at a position corresponding to the needle holder and at least partially disposed inside the needle, a cannula disposed on the cannula holder, a pivoting assembly pivotally disposed on the base, a lever movably disposed on the base and movably engaged with the pivoting assembly, an actuator disposed on the base, and a driving component for driving the pivoting assembly to pivot when the actuator slides to disengage from the pivoting assembly. When the pivoting assembly pivots, the lever drives the needle holder to slide along an insertion direction and then along a retraction direction, so as to insert the cannula into the patient's body. Besides, a medical device having the aforementioned medical insertion mechanism is also provided.