The reaction mechanism and dynamics of the laser induced excited triplet of 1,4-naphthoquinone (NQ) quenched by TEMPO and biological antioxidant vitamin C (VC) were investigated by means of time resolution electron spin resonance (TR-ESR) method. During the photolysis of NQ/EG (ethylene glycol) solution, NQ abstracts hydrogen atom from solvent molecule EG and the neutral radical NQH and EG ketyl radical CHH(OH) were generated. When TEMPO was added into NQ/EG solution, TEMPO is an effective quencher of NQ and the quenching rate constant is Lmols. For NQ/VC/EG-HO solution, NQ abstracts hydrogen atom not only from solvent EG but also from VC. VC is also an effective quencher of NQ and the quenching rate constant is Lmols. The quenching reactions of NQ by TEMPO and VC are both controlled by diffusion.