A fender fastenable to a bicycle bracing post includes at least a fender body and a fastening assembly. The fender body has a front section on which a concave portion, a slit and a holding space are formed. The slit can be opened elastically to allow a bicycle rear fork to be held in the holding space. The fastening means and the fender body can be coupled and adjusted to quickly install the fender on the bicycle bracing post. As a result more space is available to hold other bicycle accessories.