To obtain calcium hydroxide which is capable of suppressing the change to calcium carbonate and has high activity and good dispersibility to plastic and/or rubber by forming the calcium hydroxide which has a fine secondary particle size and a relatively high BET specific surface area and is subjected to a surface treatment by an anionic surfactant.

An aqueous solution of a water soluble calcium salt and an aqueous solution of an alkali hydroxide metal of an equivalent or above are mixed and reacted and thereafter, the mixture is heated and matured for about 0.5 to 4 hours at about 60 to 150°C. The anionic surfactant or a surfactant of a fatty acid salt system of 0.1 to 10 wt.% of the weight of the calcium hydroxide is added to the mixture and the mixture is surface treated. The mixture is then subjected to filtering and drying, by which the calcium hydroxide is obtained. The average secondary particle size of the resulted calcium hydroxide is desirably 0.1 to 1.5 μm, more preferably 0.5 to 1.1 μm in cumulative 50% and ≥6 μm, more preferably ≤4 μm in cumulative 905 and the BET specific surface area thereof is 7 to 20 m2/g, more preferably 10 to 15 m2/g.