Dielectric properties of one-dimensoional polymer PTS single crystal have been measured along the chain direction in the temperature rang 77-273 K. A second-order phase transition from a high temperature nonpolar state to a low temperature polar state accompanied by an anomaly in the dielectric constant is observed at 195 K. Two peaks in the dielectric loss are found at 150 K and 100 K. The results are explained by a model which invokes three modes of side group motions.