A tunable multiwavelength brillouin/erbium fiber laser with doubleBrillouinfrequency spacing based on a fourport circulator was experimentally demonstrated. The fiber laser configuration formed by fourport circulator isolates the oddorder brillouin stokes signal to circulate within the cavity only. In addition, it also allows propagation of the incoming brillouin pump and evenorder Stokes signals from fourport circulator to output coupler. A fiber FabryPerot tunable filter was used to manipulate the location of selflasing cavity and to increase power for multiwavelength oscillation. It can be obtained that a wideband tuning range and more output channels. At the brillouin pump power of 8 dBm and the 980 nm pump power of 279 mW, 6 output channels with 0.173 nm spacing and tuning range of 28 nm from 1535 nm to 1563 nm were achieved.