In this paper, the properties of the cement mortar modified with styrene acrylic ester copolymer (SAE) was investigated. Expanded vermiculite as lightweight aggregate were used for making the polymer modified mortar (PMM) test specimens. To study the effect of polymer cement ratio and vermiculite-cement ratio on various properties, specimens were prepared by varying the polymer cement ratio from 0% to 30% by mass of cement and vermiculite-cement ratio from 3 to 9 by volume of cement. For all the mixes, the water cement ratio was adjusted to maintain a constant flow between 180 mm 10 mm. Tests of physical properties such as density, water absorption, thermal conductivity were made on PMM specimens.Three-point flexure and modified cube compressive tests were also made on standard prismatic mortar specimens.