Optical buffer is a key component in all optical information processing systems. Slow light at room temperature via four-wave mixing (FWM) in semiconductor optical amplifier (SOA) is experimentally investigated. Time delay of 0.40 ns is achieved for a sinusoidal modulation signal at 0.1 GHz, corresponding to a delay bandwidth product (DBP) of 0.04. Factors that affect the experimental results are discussed. It is found out that the variable optical delay via FWM in SOA can be controlled either electrically by changing the SOA bias or optically by varying the pump power or pump-probe detuning.