Accurate slice separation for simultaneous multi-slice acquisition continues to be challenging, especially when animal scanners equipped with relatively few receiver coil elements are used. We propose an optimized slice-GRAPPA method to reconstruct the dual-band EPI of rat brains, in which the size-optimized kernel was iteratively estimated to reduce artifacts. The reconstructed images were evaluated in terms of inter-slice leakage, g-factor, and temporal variation across the repetitions. With the proposed method, inter-slice leakage artifacts and the g-factor were reduced, and the average signal-to-noise ratio was improved. Thus, the total reconstruction accuracy was improved in the multiband EPI in a small animal study.