We have investigated the thermodynamical properties of dark energy .
Assuming that the dark energy temperature T \sim a ^ { - n } and considering that the volume of the Universe enveloped by the apparent horizon relates to the temperature , we have derived the dark energy entropy .
For dark energy with constant equation of state w > -1 and the generalized Chaplygin gas , the derived entropy can be positive and satisfy the entropy bound .
The total entropy , including those of dark energy , the thermal radiation and the apparent horizon , satisfies the generalized second law of thermodynamics .
However , for the phantom with constant equation of state , the positivity of entropy , the entropy bound , and the generalized second law can not be satisfied simultaneously .