Conformational characteristics of poly(di-n-butylsilane) (PDBS), poly(di-n-hexylsilane) (PDHS), and poly(methy l-n-propylsilane) (PMPrS) have been investigated by a rotational isomeric state (RIS) scheme with molecular dynamics simulations. Characteristic ratios thus calculated for PDBS, PDHS, and atactic PMPrS are, respectively, 42.0, 54.0, and 12.3, being comparable to our light-scatterine, measurements. In the 0 state. most Si-Si bonds of PDBS and PDHS adopt deviant +/- (D+/-) conformations (dihedral angles approximate to +/- 150degrees); in adjacent Si-Si bonds, D+/-D+/- conformations are the most stable, and D+/-D-/+ states have a slightly higher energy of ca. 0.1 kcal mol(-1). This is the reason for their rigidity in solution and the formation of a disordered structure. An RIS treatment for pseudoasymmetric polymers with different side chains (R and R') (e.g., [-SiRR'-](x), and [-CRR'-](x)) has been developed. By this method, the characteristic ratio of atactic PMPrS was obtained as above, and the stereosequence dependence of the spatial configuration of PMPrS was investigated; the characteristic ratio increases with the meso-diad probability. The UV absorption maxima (lambda(max)) of PDBS, PDHS, and PMPrS were correlated with average dihedral angles evaluated from the RIS calculations. The solubility of polysilanes has also been elucidated in terms of conformation.