We present V and Ks photometry of four OGLE stars that are candidates to present transits due to extrasolar planets. This is part of a monitoring campaing for a series of OGLE stars. The visual images were taken with the FORS1 instrument at Paranal observatory in March 2006, and the infrared images were taken using SOFI instrument on NTT at La Silla Observatory in April 2005. In order to characterize the OGLE stars we construct the color-magnitude diagrams of the field where the star candidates are located. This will allow us to understand more about the nature of these stars and the conditions in which the planets candidates are exposed, and complement this work with the characterization of the transit itself.