Almond alpha-mannosidase was purified by separation on columns of DEAE-Sephadex A50 and hydroxyapatite, and characterized. Its optimum pH was approximately 3.8. It was also shown to be stable from pH 6 to 8. Its activity was stable up to 60degreesC. The thermostability of almond alpha-mannosidase at 73degreesC appeared to be superior to that of jack bean alpha-mannosidase. We examined the substrate specificity of the former toward high-mannose-type N-glycan Man(9)GlcNAc(2), and showed that the deduced trimming pathway was more diverse than that of the latter. We could use almond a-mannosidase as well as jack bean alpha-mannosidase for analysis of sugar chain structures.