Shrinkage reducing agent (SRA) is one of chemical admixtures for concrete during mixing, which was developed to reduce drying shrinkage in concrete due to low surface tension. The frost resistance of mortar incorporating the traditional type SRA could be reduced. Therefore, the modified type SRA was developed to improve the frost resistance. In this study, shrinkage properties, frost resistance, pore structure and characteristics of pore solution in the mortar using the traditional and modified types SRA were discussed. It was suggested that the characteristics of pore solution in addition to the pore structure affected the shrinkage properties and frost resistance.