We investigated photocontrol of magnetization in oxide heterostructures consisting of a perovskite manganite La0.9Sr0.1MnO3 and a titanate SrTiO3 (STO) by time-resolved magneto-optical Kerr effect measurements. On photoexcitation of STO, the magnetization of the manganite increases within 0.2 ps and persists for similar to 500 ps. This ultrafast magnetization is ascribed to rapid hole injection from STO into the manganite due to strong band bending of STO near the interface, while the long lifetime of the magnetization is attributed to a delay in electron injection to the manganite layer. The photocarrier dynamics across the interface is discussed in detail.