The effects of some commercial cellulose ethers type MHEC on some physico-mechanical properties (consistency, setting time and mechanical strength) of some mortars based on portland cement (CEM I 42.5 R), limestone filler and quartz sand were studied. It was observed that cellulose ethers increase setting time and the amount of water needed to achieve standard consistency while mechanical strength significant decreases. The intensity of these effects depends on the substitution degree of cellulose ethers and on the proportion in which they are added in mortars and less on the viscosity declared by the manufacturer.