Travelling inside the human body is an on-going scientific challenge. In this paper, we propose a new way of propelling robots inside the human body for gastro-intestinal applications actuated with the gradient field of an unmodified Magnetic Resonance Imaging (MRI) system. The robot is composed of a soft ferromagnetic head and a plastic tail attached together. This assembly is then placed in a bath of water inside an MRI system. The main field of the MRI is used to magnetize the head of the device while a gradient field is used to put the robot into motion. The oscillating magnetic gradient creates a force perpendicular to the direction of swimming and as the device drifts in this direction, the lift produced on its tail moves it in the forward direction. A study varying the length of the tail of the robot from 20mm to 80mm, the frequency applied and the amplitude of the gradient has been conducted and is developed in the following.