We demonstrate the fabrication of symmetric waveguides in a bismuth germanate (BGO) single crystal using a double line approach by an 800nm femtosecond laser. The optical attenuation of the single mode waveguide is measured to be 4.2dB/cm at 633nm. The influence of pulse energy and focal depth on the end facet of the irradiated region is also studied. This technique is promising to fabricate buried BGO waveguide arrays used in positron emission tomography systenls.