Lactose is the second most abundant component present in milk. It is commercially produced from whey or whey permeate or milk permeate by crystallization. The current problem is lack of efficient tool to monitor crystal sizes and chord lengths during industrial lactose crystallization (LC). The objective of this study was to use focused beam reflectance measurement (FBRM) as a tool for in situ monitoring of LC. A 2 × 3 factorial design was used, with temperature (20°C and 30°C) and concentration (w/w) (50%, 55% and 60%) as independent variables. Desired concentrations of lactose were obtained by dissolving commercial grade lactose in distilled water. The FBRM was placed in a batch crystallizer consisting of an overheard stirrer and a temperature-controlled waterbath. LC was monitored for 630 min using an in situ FBRM system to obtain chord length distributions (CLD) and crystal size distributions (CSD). CLD obtained from FBRM were recorded in the ranges of < 50 µm (fine crystals) and 50–300 µm (coarse crystals). At regular intervals, lactose concentration was measured using a refractometer to deduce extent of crystallization. The extent of crystallization increased rapidly during the first one hour of crystallization. The time required to reach 90% extent of crystallization at 30°C was found to be 300, 360, and 420 min for 60%, 55%, and 50% solutions, respectively. As the extent of crystallization increased, the fine crystal counts obtained from FBRM were also increased. It was observed that fine crystal counts increased with increasing supersaturated concentration (65,000 for 50% and 84,000 for 60% at 30°C) and temperature (59,000 at 20°C and 65,000 at 30°C for 60%). Square weighted CLD obtained from FBRM helped demonstrate that, as concentration increased there was a substantial decrease in chord lengths at 20°C. Mean chord lengths of lactose crystals as observed by FBRM for 60, 55, and 50% at 20°C were 39.09, 40.52, and 57.64 µm, respectively at 630 min. In conclusion, FBRM in conjunction with refractometer could be used as a potential tool for in situ monitoring of LC process.