Single phase (Sr1-x, K2x)Zr4(PO4)6, where x lies between 0.0 and 1.0, ceramic powder with a submicron scale panicle size has been synthesized successfully at calcination temperatures as low as 650-750-degrees-C by a sol-gel technique. The formation of the powder strongly depends on calcination temperature, but is independent of solution pH in the studied range. Dilatometric measurement shows an ultra-low linear coefficient of thermal expansion of 0.1 x 10(-6)-degrees-C-1 when x = 0.5 at temperature intervals of 25-1000-degrees-C. Thermal conductivity and flexural strength of the materials were determined at ambient temperature to be 1.0 W m-1 K-1 and as high as 280 MPa, respectively, indicating that this material can be an excellent candidate in many applications, especially those subjected directly to severe environments.