In this work, we report on our studies on the band structure calculations, structures, transport, and magnetic properties in two dimensional layer structured perovskite compounds Sr2−xLaxCoO4. Structure refinement results reveal that these compounds crystallized in K2NiF4-type structures with space group I4/mmm. The temperature dependence of resistivity shows a semiconductorlike behavior over a wide range of temperatures, a metal-insulator transition at 240 K, and an upturn at 160 K for the x = 1, 1.25, and 0.75 samples. A coercive field is about 1 T for the sample with x = 0.75, while it is about 0.05 T for x = 0.75 and 0.1 T for the x = 1.25 samples. A negative field hysteresis magnetoresistance in close correlation with the coercive field has been observed and can be explained by the grain boundary tunneling effect. The first-principles band structure calculations were carried out for Sr1.5La0.5CoO4 and the results indicate that the system is metallic with a high spin polarization which is responsible for the observed large magnetoresistance.