We investigate the effect of a static magnetic field on the electrical properties of thin films of porous silicon. We observe a relative variation of the resistance with respect to intensity of the applied magnetic field. This effect called magnetoresistance (MR) has been found to be negative at room temperature in the entire range of the applied magnetic field (under 8000 G). The negative MR effect depends strongly of the applied voltage and reaches up to 5% at the value of magnetic field of 8000 G. The analysis has been based on the 1D weak localization theory (WL) in diffusive semiconductors, from which a consistent picture emerges, considering the PS film as networks of quasi-one-dimensional wires. We give an explicit expression for the WL correction depending only of the phase coherence length L-phi. A good agreement is observed between experimental data and theory. (C) 2012 Elsevier Ltd. All rights reserved.