The Magic-Angle Coil Spinning (MACS) resonator allows a simple approach for nanoliter Nuclear Magnetic Resonance (NMR) detections with enhanced sensitivity and high-resolution under sample Magic-Angle Spinning (MAS). Currently, the spectral resolution acquired with MACS is not efficient for detailed characterization of semi-solids like biopsies, where sub-hertz resolution is necessary. Here, we describe the two sources of line broadening from MACS, sample temperature gradient and anisotropic magnetic susceptibility, and present a refined High-Resolution Magic-Angle Coil Spinning (HR-MACS) resonator that improves the spectral resolution. We demonstrate with the high quality HR-MACS NMR spectra of micro-nematodes and tissue biopsy, and illustrate its potential for NMR-based metabolomics of nanoliter tissue samples.