In the present study, the effect of addition of flaxseed mucilage on the physicochemical and sensorial properties of semi-fat (1. 5% fat) set yoghurt was evaluated. Yoghurt samples were incorporated with flaxseed mucilage at the levels of 0. 00, 0. 10, 0. 15, and 0. 20% and analyzed periodically for pH value, titrable acidity, viscosity, consistency, water holding capacity, syneresis, colour parameters, and sensory attributes during storage at 5 º C (1, 7, and 15 days). The addition of flaxseed mucilage in the formulation of semi-fat yoghurt significantly influenced on chemical, physical, and sensorial properties of semi-fat set yoghurt during storage period. The pH value of all the samples decreased and acid value increased during storage period. Viscosity, consistency, water-holding capacity of the yoghurt samples increased while the syneresis value decreased with increasing the amount of flaxseed mucilage and storage time. Flaxseed mucilage addition decreased L* value while increased a* and b* values of the yoghurt. The sensory attributes of yoghurt samples were also affected by the level of flaxseed mucilage, so that the sample containing 0. 15% flaxseed mucilage was preferred in terms of all the sensory attributes tested by the panelists.