Plaster and composites made up of gypsum have been widely used in building for different purposes. In this work, a new gypsum composite containing diatomite and polypropylene fibers was produced. Diatomite, fossilized of microscopic plants, was used up to 20% while fiber up to 1%. Samples with 120 x 120 x 20 mm and 40 x 40 x 160 mm size were produced to do tests. In addition to XRF, XRD, TGA and SEM investigations of diatomite, physical, mechanical and thermal test were done on produced samples. Also, Analysis of Variance (ANOVA) test were done in order to see the effect of diatomite and fibers studied on the quadratic model. It was observed that the usage of diatomite increases porosity that results in decreasing unit weight and thermal conductivity coefficient. Fibers increase mechanical properties. (C) 2016 Elsevier Ltd. All rights reserved.