The invention provides a water jacket structure of a cylinder head, and the water jacket structure can make cooling effect of a cylinder head which includes a lower exhaust collecting portion and an upper exhaust collecting portion improved. A lower water jacket of a cylinder head includes a lower/upper exhaust collecting portion cooling portion configured between a lower exhaust collecting portion and an upper exhaust collecting portion by bypassing a lower exhaust collecting portion cooling portion. Besides, cooling water flowing through the lower/upper exhaust collecting portion cooling portion is merely cooling water of the lower water jacket, and cooling water of an upper water jacket does not flow through the lower/upper exhaust collecting portion cooling portion. Therefore, in the lower/upper exhaust collecting portion cooling portion, interference may not occur in cooling water of the two water jackets to restrain smooth flowing, and cooling effects of an area sandwiched by the lower exhaust collecting portion and the upper exhaust collecting portion are further improved.