Significant different thermal properties between amorphous and semi-crystalline polymers have a great effect on the selection of proper sintering parameters and the resulting properties of the parts made by selective laser sintering (SLS) process. This paper studied the differences in the part bed temperature (T(b)), and relative density, tensile strength and dimensional accuracy of the SLS fabricated parts between semicrystalline and amorphous polymers, by measuring and comparing the laser sintering properties of polystyrene (PS), a typical amorphous polymer, and nylon-12 (PA12), a typical semicrystalline polymer. The results show that: the part bed temperatures (T(b)) of amorphous polymers and semi-crystalline polymers should he kept close to glass transition temperature (T(g)) and initial melting temperature (T(im)) respectively, which can be measured by differential scanning calorimetry (DSC), and this rule combined with trial and error experiments can determine T(b) of a polymer in the SLS process; the amorphous polymer SLS parts have very low relative densities and much lower tensile strengths than the strengths of their fully dense forms, while the semi-crystalline polymer SLS parts have higher relative densities and their tensile strengths are close to the strengths of their fully dense forms; the dimensional accuracy of the SLS parts of amorphous polymers is higher than that of semi-crystalline polymer SLS parts at the same processing parameters. The obtained results will be helpful for the development of new SLS materials and the setting of processing parameters.