A slew rate boost circuit for an output buffer and an output buffer circuit for a source driver having the same are provided. In an output buffer including a pull-up unit providing a buffer output signal in a first level by receiving a buffer input signal and performing pull-up operation and a pull-down unit providing a buffer output signal in a second level having opposite phase from the first level by receiving the buffer input signal and performing pull-down operation, the slew rate boost circuit includes a first comparator generating a first boost signal to boost pull-up operation of the pull-up unit of the output buffer by inputting a first input signal and a second input signal and a second comparator generating a second boost signal to boost pull-down operation of the pull-down unit of the output buffer by inputting the first input signal and the second input signal.