© COPYRIGHT SPIE. Downloading of the abstract is permitted for personal use only. It is of vital importance to understanding the relation between image quality and excitation light pulse characteristics in LED-based photoacoustic imaging system. We have tried to change pulse waveform of LED light source to detect several kinds of photoacoustic signals related to the image quality. As a result, in order to understand the photoacoustic signal, it is necessary to consider the characteristics of the optical pulse waveform and the ultrasonic probe well.