We have investigated the transport and magnetic properties of the spin-1/2 ladder system with two legs, Sr14-xAxCu24O41 (A = Ba and Ca). For x - 0, the electrical resistivity ρ exhibits semiconductive behavior. It becomes more insulating with the increase in x(Ba), while it becomes more conductive with the increase in x(Ca). The broad peak of the magnetic susceptibility around 80 K has been studied in detail. Subtracting the Curie component at low temperatures, the remainder of the susceptibility Xs(T) decreases towards zero with decreasing temperature below ∼ 80 K, which implies the presence of a spin gap. The value of Xs(T) decreases with the increase in x(Ba), while it tends to increase with the increase in x(Ca). Moreover, for the samples with x = 0 annealed under various atmospheres, p tends to decrease and Xs(T) increases with the decrease in oxygen content. These properties are discussed in terms of the redistribution of holes between the two different sites of Cu. It seems that the observed spin-gap behavior is due to Cu2+ spins in the CuO2-chain rather than in the Cu2O3-plane.