In this study, a method for assigning optimal tolerance values for the circuit parameters is suggested when one or more tuning components exist in the circuit. Component tolerances are optimized on the worst case basis (or 100\% yield) by using nonlinear programming from a viewpoint of continuous tolerance value and by the method of tolerance extension by tuning. And also, design centering problem is s ved simultaneously with tolerance optimization. As an example, an active RC equalizer is considered and its results are shown.