Some fuzzy rule interpolation methods have been presented for sparse fuzzy rule-based systems based on interval type-2 fuzzy sets. However, they have the drawbacks that they can not guarantee the convexity of the fuzzy interpolated result and may generate the same fuzzy interpolated result with respect to different observations. In this paper, we present a new method for fuzzy rule interpolation for sparse fuzzy rule-based systems based on the ratio of fuzziness of interval type-2 fuzzy sets. It can overcome the drawbacks of the existing methods. We also use some examples to compare the fuzzy interpolated results of the proposed method with the results by the existing methods. The proposed fuzzy rule interpolation method gets more reasonable results than the existing methods.