A series of poly(alkyl(methoxyphenyl)silane) homopolymers and poly [(alkyl(methoxyphenyl)silane)-co-((S)-2-methylbutyl(methoxyphenyl)silane)I copolymers containing 20%. chiral monomer units were synthesized, and marked substituent effects on their absorption characteristics and the global and local conformations in THF solution were observed. In the homopolymers, upon increase of the alkyl side chain length, the global backbone conformations changed from a considerably shrunken random coil to a stiff extended structure, and the UV absorptivity and absorption wavelength maximum in the Si main chain region were easily controlled by a combination of the alkyl substituents and position of the methoxy group on the phenyl ring. In the achiral-chiral copolymers, preferential screw-sense helical conformations of the Si backbone were induced by the cooperative effect of the chiral substituents. In addition, we found that the sign of the circular dichroism (CD) peak in the aryl absorption region of the copolymers depended on the methoxy group position in chiral monomer units.