In this study; important mechanical and physical properties of cement composites prepared with fine aggregate and coir fibers were investigated. In addition to control mortar mixtures without fiber addition, coir fiber incorporated composites were prepared by adding 0.4%, 0.6% and 0.75% coir fiber by weight of total mixtures, respectively. The effect of coir fibers on the mechanical properties of composites under compressive and flexural loads, water absorption capacity and thermal conductivity of mortars were investigated. Moreover, similar mixtures were prepared with alkali treated coir fibers having same ratios and the findings were discussed. As a result, fiber incorporation affects water absorption capacity of mortars, enhances their mechanical and thermal properties and decreases their unit weight. These effects become more significant by increasing amount of fibers and when alkali treated coir fibers are replaced with untreated ones. (C) 2014 Elsevier Ltd. All rights reserved.