We present an investigation of electrical transport through fused and orthogonal dithiolated porphyrin arrays of different molecular lengths. Length dependence measurements show that conductance decreases much more slowly with molecular length than the exponential dependence expected for a coherent tunneling process. It suggests that the electrical conduction through porphyrin arrays is mainly due to the thermally activated hopping transport. From the temperature dependence of I-SD-V-SD curves, the thermal activation energy Ea is estimated to be about 0.35 eV at zero-bias voltage, independently of molecular conformation and length. (c) 2005 Elsevier B.V. All rights reserved.