9-fluorenone 0.7 g was then added to the reaction liquor thus obtained, and the liquor was heated to 55°~60° C. Thereafter, glucose 6.0 g was added to the reaction liquor over 30 minutes, and the reaction was conducted at 75° C. (boiling point) for 6 hours. As this result, the N-oxide disappeared, thus Process (c) being completed. Thereafter, pH of the reaction liquor was made to 8 with 62% sulfuric acid 19.0 g to precipitate a crystal. The precipitated crystal was separated by filtration, and the separated crystal was fully washed with water and further with methanol. The washed crystal was then dried, thus obtaining 11.6 g of 2-(2'-hydroxy-5'-t-butylphenyl)benzotriazole.
