An inkjet ink set including: an ink composition including water, a colorant, polymer particles having a glass transition temperature of 90° C. or higher, an organic amine and an inorganic salt; and a treatment liquid that includes an acidic compound and generates aggregation when comes into contact with the ink composition. The inkjet ink set and an image forming method using the same provide preservation stability and secured excellent jetting ability of the ink composition, and an image having image quality with suppressed formation of satellite droplets.