Micromixers are one of the key parts in microfluidic devices. Therefore, passive micromixers have become a popular research topic. In this thesis, parametric optimization of a Y-shaped micromixer with mixing chamber is documented. Design parameters are; alpha () for the angle between the two inlet angles, beta () for the angle between the z axis and one of the inlet channels and theta () for the angle between the other inlet channel, z-eccentricity (zecc) is the distance between the centerline of an inlet channel and origin of the mixing chamber along z-axis, x-eccentricity (xecc) is the distance between the intersection point of the two inlets and the origin of the mixing chamber along x-axis, ratio of the inlet and outlet channel length (L1/L2), ratio of the inlet and outlet channel diameter (D1/D2), ratio of the inlet channel length and diameter (L2/D2) and ratio of mixing chamber volume to the total volume(Vsp). = 180o - 240o range and zecc= 20m corresponds to the optimal range. Effect of each parameter on the system is discussed and the best performing 3 mixer designs are further investigated. The optimized design yields 88.16% mixing efficiency with 9244.4 Pa pressure drop when Reynolds number is 81. Furthermore, performance of this design is compared with a reference design. The comparison shows that optimized design decreases the pressure drop more than 50% for all Reynolds numbers while having a higher mixing efficiency (up to 35%) with low Reynolds numbers (0.054-3).