The different water soluble ink-jet inks based on conjugated poly (3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) were formulated with various organic co-solvents such as diethylene glycol (DEG), triethylene glycol (TRIEG), tetraethylene glycol (Tetra EG), and polyethylene glycol (PEG) to print on the flexible substrate. The effect of adding various organic co-solvents, which show a same trend of molecular weight, dipole moment and boiling point on the formulated inks properties and ink-jet printed films electrical conductivity, morphology and transparency were investigated. The conductivities of the ink-jet printed films were evaluated by four-point probe conductivity measurement. The morphologies of the printed films have been studied using atomic force microscopy and scanning electron microscopy. The size of PEDOT:PSS particles and the printed film morphology altered by addition of different types of co-solvent in the ink-jet ink formulation. The electrical conductivity of the ink-jet printed film increased by raising the molecular weight, boiling point and dipole moment of used co-solvent in ink-jet ink formulation.