An electrochemiluminescence (ECL) sensor was constructed with graphitic carbon nitride nanosheets (g-C3N4 NSs) as the luminophor and multi-walled carbon nanotubes (MWCNT) as signal amplifier. It was interesting to find that the ECL signal could be quenched by epinephrine (EP) and the variation of ECL signal was linearly related to the concentration of EP. Based on this finding, a simple and sensitive method for the determination of EP was established. The quenching mechanism of EP on the ECL system is discussed.