Effective interactions between excitons and resonating nanocavities are important for many emerging applications in nanophotonics.Although plasmonic nanocavities are considered promising substitutes for diffraction-limited dielectric microcavities,their practical applications are hindered by large ohmic loss and Joule heating.Other than plasmonic materials, highrefractive-index dielectric nanocavities is a new way to trap light in subwavelength scales.However, studies on the interaction between dielectric nanocavities and excitons are still scarce.Here, for the first time, we demonstrate that the Fano interference between molecular excitons and an individual silicon nanogroove can generate scattering dark modes.By placing J-aggregate excitons into a silicon nanogroove, the leaky magnetic resonant modes filling in the groove can tailor their scattering directivity and reduce the uncoupled radiation decay in a specific direction.This unidirectional’dark state’brings a new approach to tailor the interaction between excitons and nanocavities without large near-field enhancement.By adjusting the resonant modes, the scattering spectra can change from a Fano asymmetric line shape to a significantly suppressed scattering dip.These findings indicate that silicon nanogrooves can provide a platform for integrated on-chip silicon-exciton hybrid optical systems in the future.