This study was aimed to evaluate the effect of galactomannan mucilage (0–2%) extracted from wild sage seed on the growth of Lactobacillus caseiand the potential of this mucilage in combination with alginate, as an encapsulating agent, for protecting L. caseiunder gastrointestinal conditions. For this purpose, wild sage seed mucilage (WSSM) was extracted and its extraction yield and monosaccharide components were determined. Then, the effect of WSSM (0–2%) on the growth of L. caseiin MRS broth and MRS agar was investigated. Finally, L. caseiwas encapsulated by a mixture of sodium alginate (2%) and WSSM (0, 0.5, 1, and 1.5%) using the emulsion technique and their thermal properties, zeta potential as well as their stability in simulated gastrointestinal conditions were studied. According to the results, WSSM had a relatively high extraction yield (12.31 ± 0.98%) and the most important monosaccharides in its structure were galactose and mannose. This mucilage had a stimulatory effect on the growth of L. casei. The mean diameter of the microspheres and their negative charge significantly increased by adding WSSM (P< 0.05). According to the differential scanning calorimetry results, the addition of WSSM significantly increased the melting enthalpy, melting temperature, and glass transition temperature of microcapsules (P< 0.05). Moreover, it was observed that the addition of WSSM significantly improved the resistance of L. caseiagainst gastrointestinal conditions (P< 0.05). However, no significant difference was observed between the microcapsules containing 1 and 1.5% WSSM (P> 0.05).