Mezquite seeds are a good source of polysaccharides called galactomannan. The method for galactomannan extraction has been standardized by using autoclave for time intervals of 5, 10 and 15 minutes at 121°C with different endosperm:water ratios 1:10, 1:20 and 1:30 (w/v). The optimum yield obtained was 17%. Physicochemical characterization was done and structural properties of extracted material have been determined by FTIR and proton NMR. Polysaccharides extracted were assumed to be galactomannans according to the literature. Thermal parameters showed no significant changes on theirs properties. The standardized method can be scalable to industrial process.