A colored toner for developing electrostatic images which has a degree of gelation of 2.0% or less and comprises an association of secondary particles containing polymer particles having acidic polar groups or basic polar groups and an organic pigment and/or an organic dye treated with a treatment agent containing a surface treatment agent which has the same ionic character as the polymer particles so that the absolute value of .zeta.-potential becomes 10 to 100 mV at pH 5, and a developer for electrostatic images which comprises this colored toner and a carrier.