Unperturbed chain dimensions of poly(di-n-hexylsilane) (PDHS), poly(methyl-n-propylsilane) (PMPrS), and poly(di-n-butylsilane) (PDBS) have been evaluated by a combined use of static light scattering, size exclusion chromatography (SEC), and SEC-multiangle laser light scattering. The a solvents and characteristic ratios (C-infinity's) of the individual polysilanes were determined as follows: PDHS, a mixed solvent of n-hexane (58.2 wt %) and 2-propanol (41.8 wt %) at 25 degreesC and C-infinity = 42.5; PMPrS, a mixed solvent of n-hexane (62.6 wt %) and 2-propanol (37.4 wt %) at 25 degreesC and C infinity = 19.9; PDBS, n-hexane at 19.1 degreesC and C-infinity = 42.3. These C infinity values show that the polysilanes in the theta state are much more extended and rigid than ordinary carbon backbone polymers. On the basis of the results, the conformational characteristics of the three polysilanes are discussed by reference to their UV spectra.