The smectic liquid crystal arrangements of binary mixtures of rod-like polymers, i.e., poly[n-(decyl-(S)-2-methylbutylsilane]s, with narrow molecular weight distributions, were investigated by synchrotron radiation small-angle X-ray scattering (SR-SAXS) and atomic force microscopy (AFM) analyses. Depending on the molecular weight ratio, r (higher molecular weight/lower molecular weight), and the mixing ratio, three types of smectic phases are formed with different accommodations by two polymers. In the binary Mixture of the shorter and longer polymers with the lower r values of 1.0-1.7. the two polymers are randomly mixed within a layer, forming the conventional smectic A1 phase with a layer thickness corresponding to,in average length of the two polymers. In contrast, when two kinds of polymers with the higher r Values of 1.7-2.8 are mixed, different types of smectic A structures are formed. Upon the addition of the shorter polymer to the abundant longer polymer, a smectic A2 phase in which a pair of smectic layers of shorter polymers nested in a smectic layer of the longer polymers was first formed, and then converted into the smectic A3 phase in which the longer polymers randomly straddled a pair of smectic layers of the shorter polymers. These experimental results are discussed along with a comparison of the theoretical predictions.