In this research, the mechanical properties of cement based mixtures with glass fiber were compared with plain blend. In this study, a type II portland cement and a calcium aluminate cement have been used. In order to investigate the mechanical characteristics, the tests including compressive strength, the flexural strength, toughness and impact resistance of the mixtures were evaluated at ages from 28 days to 90days. Glass fiber was incorporated in the mixes at replacement levels of 2 and 4 percent (percent of the total volume of the mixture). Based on the results, the fiber-reinforced mixtures had higher flexural strengths compared to the plain mixture (fiber-free mixture) and by increasing the percentage of glass fiber, the final flexural strength was increased, however the glass fibers had little effects on the compressive strength compared to the plain mixture. It was also observed that by adding fibers the toughness and impact resistance of the specimens were also improved.