Abstract: A method for operating an output buffer for reducing a power/ground bounce noise while maintaining high transmission rate is disclosed. The method includes steps of providing a plurality of driving current paths to an output end of the output buffer when an output end of the output buffer is switched from a low level to a high level, turning off a portion of the driving current paths when the output end of the output buffer is kept at the high level, providing a plurality of discharging current paths to the output end when the output end of the output buffer is switched from a high level to a low level, and turning off a portion of the discharging current paths when the output end of the output buffer is kept at the low level. In addition, an output buffer with both low power/ground bounce noise and high transmission rate is also disclosed.