A wavelength tunable plastic laser with asymmetric distributed Bragg reflectors (DBRs) is proposed. This device consists of a pair of long-period waveguide gratings and a polymeric active waveguide doped with an organic dye. Due to the difference in grating periods between the two DBRs, the lasing wavelength can be tuned in accordance with a Vernier effect of the resonance between the reflection wavelengths. The plastic laser device operated with this principle has promise as a compact and widely tunable light source because a large wavelength shift in a wide emission band of an organic luminescent material can be expected with a small variation in the effective index.Index Terms-Distributed Bragg reflector, plastic laser, wavelength tuning.