Detailed chemical, structural and spectroscopic properties of jarosite solid solution minerals are key information for their potential discoveries by future remote sensing and in-situ detections on Mars. We successfully synthesized seven homogeneous K–Na jarosite solid solutions under hydrothermal conditions at 140°C, whose phase identifications and chemical compositions are confirmed by X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS). The chemical ratios of K/(K+Na) in jarosite solid solutions lead to systematic shifts of their characteristic Raman peaks ν1 (SO4)2− (from 1006 to 1011.3cm−1), ν3 (SO4)2− (from 1100.6 to 1111.2cm−1), ν2 (SO4)2− (from 434.2 to 444.8cm−1) with the increase of Na content. While the OH stretching mode decreases with even larger peak position variations (e.g., ∼3410cm−1 peak shifts from 3410.5 to 3385.7cm−1) as the K–Na jarosite solid solutions are enriched in Na content. Raman spectroscopic measurements of the seven K–Na jarosite solid solutions enabled us to build a calibration that uses Raman peak positions to estimate K–Na variation in jarosite, which is the key step for their possible applications in the future Raman applications on Mars' missions (e.g., ExoMars and Mars 2020 missions). The band assignments and compositional related variations of their XRD, near-infrared (NIR) and mid-infrared (MIR) spectra also provide informative clues for identifying the jarosite minerals and inferring their composition during martian in-situ and remote sensing measurements.