Retinal prosthesis has been developed for the patients with retinitis pigmentosa (RP) and age related macular degeneration (AMD), and is regarded as the most feasible method to restore vision [1-2]. Extracting optimal electrical stimulation parameters for the prosthesis is one of the important prerequisites for the success of retinal prosthesis. Previously, we proposed the optimal stimulation parameter range (e.g. amplitude, duration) for evoking retinal ganglion cell (RGC) responses using rectangular pulse shape in wild-type and rd1 mice [3]. Traditionally, rectangular pulse shape has been the choice for neural stimulation. Not much attention has been paid to alternative pulse shapes. Therefore, we investigated pulse shape effect on evoking RGC responses. The well-known animal model for RP, rd1 (Pde6b rd1 ) mice [4] at postnatal 8 weeks and after were used. From the ex-vivo retinal preparation, retinal patches were mounted on planar 8×8 microelectrode array (MEA), ganglion cell layer down onto the MEA mimicking the epiretinal prosthesis configuration. While applying current stimulus through one channel of MEA, retinal waveforms were recorded with remaining channels of MEA. Biphasic-charge balanced current pulses in the form of cathodic phase-1st and anodic phase-2nd were applied once per second (1 Hz, x 50). We tested 3 different pulse shapes with same charge; 1) biphasic rectangular pulse (I: intensity, D: duration), 2) biphasic triangular pulse with double intensity (2xI, D), 3) biphasic triangular pulse with double duration (I, 2xD). For intensity modulation, duration of the pulse was fixed to 500 μs and the intensities of the pulses were modulated from 5 to 40 μA. For duration modulation, pulse amplitude was fixed to 30 μA and the pulse durations were modulated from 60 to 500 μs. The electrically-evoked RGC spikes was defined as positive when the number of RGC spikes for 400 ms after stimulus was 1.3 times higher than that for 400 ms before stimulus in post-stimulus time histogram. RGC responses were well modulated both with rectangular and triangular pulse by varying the amplitude and duration of the pulse. Amplitude modulation shows that RGC response is preferentially activated by biphasic triangular pulse with double duration especially with 5 and 10 μA amplitude (p<0.001). Duration (D) modulation shows that RGC response is preferentially activated by triangular pulse with double duration especially with 60 and 100 μs (p<0.001), while triangular pulse with double amplitude is most efficient at 200 μs pulse duration (p<0.001). Now, we are comparing the stimulus threshold among three different pulse shapes in this study.