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The high risk of solution-mediated phase transformation (SMPT) from the metastable monohydrate to stable Form I makes it difficult to produce pure metastable monohydrate of calcium D-gluconate. In this work, we explored the effect of various operating parameters on the SMPT of calcium D-gluconate in water and proposed an effective approach to obtain the desired monohydrate. First, the two forms of calcium D-gluconate were characterized and compared using powder X-ray diffraction (PXRD), thermal analysis, and Raman spectroscopy. The lower solubility of Form I in water illustrates its higher thermodynamic stability than monohydrate when the temperature is higher than 292 K. Afterward, the SMPT of calcium D-gluconate from monohydrate to Form I was investigated in water using in situ Raman spectroscopy combined with scanning electron microscopy and PXRD. Results showed that the nucleation and …