Provided is an annealing separator with which a grain-oriented electrical steel sheet having a forsterite film with excellent appearance uniformity and adhesion can be obtained. The annealing separator for grain-oriented electrical steel sheet comprises: magnesia that contains 0.05 mass % or more and 0.20 mass % or less of B and 0.01 mass % or more and 0.10 mass % or less of P, and titanium oxide in 1.0 part by mass or more and 10.0 parts by mass or less per 100 parts by mass of the magnesia where the titanium oxide contains one or more types of alkali metals in a total amount of 0.0050 mass % or more and 0.50 mass % or less, where an amount of P adsorbed on per 1 g of the titanium oxide is 1.5×10−4 g or more and 1.0×10−3 g or less.