We propose an opto∞uidic based on two-dimensional (2D) rod-type silicon photonic crystal (PhC) waveguide that supports self- collimation efiect over a large frequency and angle range without any defect or nano-scale variation in the PhC geometry. By analyzing the equi-frequency counter (EFC) of a triangular rod PhC-bands, we verify the optimum band of the structure which is suitable for self- collimation of light beams. By varying the refractive index of ∞uid being inflltrated into the background of PhC, we perform a systematic study of opto∞uidic self-collimation of light beams to achieve a wide range of angles and low loss of light. By means of selective micro∞uidic inflltration and remarkable dispersion properties, we show that it is possible to design auto-collimatator and negative refraction devices based on self-collimation efiect with high transmission. We use the plane wave method (PWM) for analyzing the EFC and the flnite difierence time domain (FDTD) method for simulating the transmission properties.