In this paper was studied kinematic design of a three degrees of freedom (dof) planar mechanism. The mechanism was desired to be applied as an assembling equipment composed of three identical kinematic chains connected platform as an output motion and base as a fixed link. The kinematic chains were constructed by three revolute joints (RRR). The platform of mechanism performs three dof planar motion consisting of two dof translational motion and one dof rotational motion. Kinematic constants of the mechanism was determined based on workingspace, singularity and dexterity. There are four kinematic constants of the mechanism consisting of link lengths of kinematic chain, L1, L2, distance between mounting two joints in the base, sb and distance between mounting of kinematic chain to platform and center of platform, rP. To simplify, the kinematic chain was designed identically and all kinematic constants was normalized with respect to sb. It was proposed three synthesis steps to obtained set of kinematic constants. They are evaluation of available workingspace, determination of effective workingspace which is free from singular point and evaluation of dexterity indicating the ability of platform to change its orientation in specific position. Based the work, it was obtained the optimal set of kinematic constants represented by L1 = L2= 0.3sb, rP = 0.2rB and sb = 1 unit. Using the such as configuration of kinematic constants, 3-RRR planar parallel mechanism can move translationally in area 0.124 square unit without considering the change of its orientation called as an effective workingspace. Then the platform can change its orentation, 40 degree in area 50% of effective workingspace. Key words : Kinematic design, dimensional synthesis, planar parallel mechanism, workingspace, singularity, dexterity.