The aim of this study was to investigate the compositional, rheological and organoleptical characteristics of Labneh made by ultrafiltration as affected by partial substitution of milk solids with whey protein concentrate powder (WPCP). Labneh based on 26% total solids (TS) and 0.5% NaCl was made from buffaloes' milk retentate concentrated by ultrafiltration. The milk solids in the retentate was partially substituted with WPCP at the levels of 0, 10, 20, 30 and 40%. The results indicated that the fat and lactose contents as well as pH values of Labneh decreased with increasing the ratio of WPCP. However, the protein content, ash, titratable acidity (%)increased with increasing the added amount of WPCP. The Labneh consistency coefficient and the yield stress were obviously increased as the level of WPCP increased. During cold storage of Labneh, its acidity and diacetyle contents increased up to 21 days, while acetaldehyde content increased up to 7 days of cold storage then decreased thereafter. Organoleptically, the Labneh quality was improved by adding WPCP with all of the examined levels, and remained acceptable during cold storage up to 21 days. Thus, milk solids in UF buffaloe's milk retentate could be substituted by WPCP at level of 30% in Labneh made with acceptable quality at lower cost.