Biological objects were micromanipulated with a magnetic microactuator. These objects are pushed with a small ferromagnetic particle whose size can be as small as 10£ 10£ 5 ¹m3. This particle is called the manipulator and is moved thanks to a permanent magnet. This magnetic device allows the manipulation of objects in an extremely confi ned space. As biological objects are fragile, the force applied on them must be controlled during the manipulation. The model we present allows to determine the force applied by the device on the manipulated object. Several experimental measurements are presented in order to validate the model.