We have synthesized new organic superconductors θ- and κ-(BEDT-TTF)2I3, which have two dimensional electronic structure with the Fermi surface isotropic in the 2D plane. This paper deals with the anomalous magnetoresistance effect observed in the normal state, which is summarized as follows. 1. The magnetoresistance is a linear function of the magnetic field. 2. It depends on the magnetic field direction relative to the crystal axis and does not depends on the current direction.