In the present work, the effect of wettability on CaCO 3 precipitation was approached by monitoring crystal formation in microchips of different wettability degree. Solutions of calcium chloride and sodium bicarbonate were mixed in hydrophilic and neutral-wet Y-junction microchips, and the precipitation of CaCO 3 crystallites was monitored. Sequential pictures showed the formation and growth of CaCO 3 crystals as a function of time, and the precipitates were identified by Raman spectroscopy. The obtained results indicated that in hydrophilic microchips, the increase of supersaturation ratio value resulted in higher growth rates and aggregate formation. The neutral-wet microchip surfaces were found to accelerate the precipitation of CaCO 3 compared to hydrophilic surfaces, and in the case of neutral-wet surfaces, crystallites were formed mainly close to the wall surfaces. In hydrophilic microchips, calcite was the main precipitate, while aragonite formation was favored in neutral-wet microchips.