A micro-scale technique has been developed for the process development of transaminase catalysed reactions. This pH indicator based, colorimetric assay can be used to investigate and optimise reaction conditions at 100 μL scale. Enzyme activity and stability as a function of various reaction parameters, including temperature, pH and co-solvent concentration, have been determined. Additionally, reactions have been scaled up from 100 μL to 25 mL under the optimal reaction conditions identified by the micro-scale process development activities. Excellent conversion (>99%) and enantioselectivity (>99% ee) were obtained.