The paper studies the influence of addition of viscosity enhancing biopolymers (diutan gum, gellan gum, xanthan gum, carrageenan, and sodium salt of alginic acid) in the doses of 0.1%, 0.5% and 1% on the fresh state, and physical-mechanical properties of hardened mortars. The mortars were prepared with the constant water/binder ratio and the binder/aggregate ratio of 1:3 by weight. The properties have been studied after 7 and 28 days of curing time. All the admixtures, with the exception of gellan gum, improved workability (by lowering the value of spread) in comparison with reference mortar. Most of them also increased the amount of air on the fresh mortar, thus decreasing the density of fresh mortar and also the bulk density of hardened specimens. The addition of biopolymers caused certain decrease of strengths, but there was observable trend of decreasing difference between the reference and tested mortars with the increasing amount of time.