Cellulose regeneration is a critical step in the production of textiles, cellulose derivates, edible films for packaging or biomedical products because the regeneration process alters the cellulose properties. Cellulose regeneration involves complex intermolecular interactions and kinetics that determine the structure and properties of the regenerated cellulose products. Homogeneous quality is crucial for meeting market demands, but it is challenging due to variations in raw materials, process conditions, and other factors. On-line real-time monitoring of the cellulose regeneration process will allow researchers to optimize the process and producers to assess and control the key parameters involved during the regeneration process, ensuring both optimal product quality and process efficiency. This paper describes for the first time the potential of using focused beam reflectance measurements (FBRM) to monitor the evolution of cellulose regeneration under different conditions. The analysis of the evolution of the cellulose particle growth under different conditions allow us to confirm that the mechanism of cellulose aggregation is initiated by hydrophobic interactions and to understand the contribution of the different processes involved during the regeneration such as nucleation, particle growing, cellulose flocculation and floc break down. The results indicate that hydrolysis of urea in alkaline conditions, accelerated by elevated temperatures, has a major impact on the regeneration process confirming the idea that urea prevents hydrophobic interactions. The effects of temperature, initial cellulose concentration, seeding and aging have been quantified. FBRM analysis offers crucial insights that enhance understanding of the regeneration process, enabling its optimization and facilitates the creation of customized cellulose-based materials tailored for specific applications.