A fittable and releasable fastener includes a head which has a fitted and released portion and a fastening portion; and a fitting and releasing piece which has a fitting and releasing portion. Accordingly, when the fitting and releasing portion fits to the fitted and released portion, an external turning force is applied to the fitting and releasing piece or the head to make the fastening portion combine with at least one object. After the fastening portion is combined with the object, the fitting and releasing portion would release the fitted and released portion to limit the force or the force interval applied on the fastening portion for preventing excessively locking if the force is continuously applied.