It is intended to provide a dental plaque detection system and a dental plaque detection method whereby dental plaque can be detected at a high accuracy while relieving the staining in parts (interdental space, gingiva, etc.) other than dental plaque. This dental plaque detection system comprises a dental plaque-staining agent containing at least one member selected from among a yellow pigment originating in red koji mold, a turmeric extract and curcumin and a light-emission unit (10) emitting light of from 250 to 500 nm in wavelength toward a subject (40) in the oral cavity having the dental plaque-staining agent attached thereto. The dental plaque detection method comprises attaching the dental plaque-staining agent having the composition as described above to a subject in the oral cavity and then irradiating the subject with light of from 250 to 500 nm in wavelength.