Based on the fact that optical tweezers (OT) constitute a flat system, with flat outputs given by the horizontal and vertical position coordinates of the geometric centre of the laser beam, a flatness-based control strategy for the manipulation of a microscopical particle is presented in this article. The control strategy is derived under the assumption that the particle is suspended in a frictionless medium, obtaining a simple controller with a relatively simple stability analysis. The control strategy is tested by tracking a straight line, an elliptic curve, and carrying out the rest-to-rest transfer manoeuvre task by using a smooth trajectory.