An oscillating scalar field as a quintessence model for dark energy is proposed .
The case of a power-law potential is particularly intriguing and is the focus of the present article .
In this model the equation of state w _ { \textsc { oq } } of dark energy is a constant determined simply by the power n in the potential through w _ { \textsc { oq } } = ( n - 2 ) / ( n + 2 ) .
Accordingly , when 0 < n < 1 , the oscillating quintessence can provide repulsive gravity and drive the cosmic acceleration .
The condition for oscillation and the constraints from observations are investigated .
For this new scenario a specific natural model with much less fine tuning is presented .