Fuzzy set theory was used to study the relationship between the glass-transition temperature (T-g) and structure of homopolymers. The method can map the relationship and give the T-g for 235 polymers with a standard deviation of 8 K (the confidence bound was 90%). The entropy of the fuzziness was used to quantitatively describe the interactions among groups. The method was used to predict the T-g of 10 polymers not included in the 235 polymers, with a standard deviation of 9 K (the confidence bound was 90%). The study demonstrates again that fuzzy set theory can be effectively used to investigate the quantitative structure-property relationship of polymers.