We demonstrate a mode locked fiber laser based on single wall carbon nanotubes. The mode locking is achieved by the evanescent field interaction of the propagating light with a single wall carbon nanotubes saturable absorber in a microfiber. The pulse width is 114fs. The maximum average output power is 21mW. The center of the wavelength is 1556nm with 26nm spectral width. The repetition rate is 111.6MHz. Keywords: Ultrafast lasers; Mode locked lasers; carbon nanotubes.