On designing the rectifying inspection plans of double sampling, the relations of the sample sizes $n_1$, $n_2$ and the acceptance numbers $c_1$, $c_2$ are obtained by using the Chi-square distribution. As the average number of pieces inspected per lot is a function of $c_1$ and $c_2$, the optimal solution is the values of $c_1^*$ and $c_2^*$ for which the average amount of inspection is a minimum. Then the values of $n_1^*$ and $n_2^*$ are easily obtained from the equations given by ($n_1$, $n_2$) and ($c_1$, $c_2$).