This article examines the in situ characteristics and behaviour of particles during palm olein crystallisation using Focused Beam Reflectance Measurement (FBRM). Melted palm olein was isothermally crystallised at 9ºC, 13ºC and 15ºC for 6 hr in a stirred, jacketed vessel and changes in crystal size, population and behaviour were tracked using FBRM. Results indicate that the induction time for primary nucleation for palm olein increased while crystal population was significantly lower at higher temperatures, as expected. Crystallisation occurred in a two-step manner at 9ºC and 13°C while a single step crystallisation was observed at 15°C. These occurrences were plausibly due to the lower super cooling and fewer species of triacylglycerols capable of crystallising at higher temperatures. FBRM detected major agglomeration of crystals at 9°C due to increased crystal population and contact between crystals. Chord length distributions (CLD) showed that the final mode crystal size was 32 μm at 9°C while significantly larger crystals of 108 μm were observed at 15°C. Microscopic observations revealed that crystals within the slurry appear gel-like below 13°C. This study extends current knowledge on FBRM application for in situ particles characterisation in real time within a palm-based crystallisation system.