A toner for developing an electrostatic image comprising: a colorant-containing particulate resin and a treated fine powdery material prepared by treating fine powdery titanium oxide with a silane-type organic compound, said fine powdery titanium oxide containing 85 to 99.5% by weight of a TiO2 component and 0.5 to 15% by weight of a Ti(OR)m (OH)n component, where R is a hydrocarbon group, m and n