Pansharpening aims to generate high-resolution multispectral (MS) images by fusing panchromatic (PAN) images with corresponding low-resolution MS images. However, many existing methods struggle to fully capture spatial and spectral interactions, limiting their effectiveness. To address this, we propose a novel quaternion-based spatial-spectral interaction network that enhances pansharpening by leveraging the compact representation capabilities of quaternions for high-dimensional data. Our method consists of three key components: the quaternion global spectral interaction branch, the quaternion local spatial structure awareness branch, and the quaternion spatial-spectral interaction branch. The first applies the quaternion Fourier transform to convert multi-channel features into the frequency domain as a whole, enabling global information interaction while preserving inter-channel dependencies, which aids spectral fidelity. The second uses a customized spatial quaternion representation, combined with a window-shifting strategy, to maintain local spatial dependencies while promoting spatial interactions, which helps inject spatial details. The last integrates the two pathways within the quaternion framework to enrich spatial-spectral interactions for richer representations. By utilizing quaternion’s multi-dimensional representation and parameter-sharing properties, our method achieves a more compact and efficient cross-resolution, multi-band information integration, significantly improving the quality of the fused image. Extensive experiments validate the proposed method’s effectiveness and its superior performance over current SOTA techniques. Code will be publicly available.