This paper presents results of experimental investigations conducted on old baked clay bricks of Indus Valley civilization of tenth century. The object of this study is to evaluate the effect of age and environmental conditions on the strength of the baked clay bricks which are about 1000 years old. The brick samples were collected from six different archeological sites at the banks of old route of River Indus in district Sanghar, Sindh, Pakistan. These specimens were tested for apparent density, compressive strength, tensile strength, modulus of rupture and the weathering effects on them during the course of time. ASTM (American Society for Testing and Materials) standard for baked clay bricks, based on compressive strength, suggests that the bricks of four sites can withstand severe weathering while the bricks of two sites are resistant to moderate weathering. These results were compared to the values of the corresponding data of bricks, of same period, obtained from the historical monuments of the world as reported in the literature. The comparison showed that the values of physical properties of old baked clay bricks of Indus valley civilization of tenth century are in agreement with that of old baked clay bricks of contemporary era. The results of this study could also be helpful for preservation of old archeological sites of Indus valley civilization.