Chemical etching rates of BPDA/PDA/ODA/BMI polyimide film by an alkaline etching solution with the presence of different kinds of etchants were studied by film-thickness measurement and UV absorption spectroscopy of dispersible etching residue. The etching rate of polyimide film in alkaline ethylene diamine solution is highest among the etching solutions studied in the present experiment. If an external bias voltage was applied during etching, the etching rate was increased. The effects of temperature, solubility of the etchant, and ultrasonic vibration on etching rate are also discussed. The presence of a radical in the process of etching reveals that the etching reaction is a type of radical chain reaction.