In this work synthesis procedures for controlling particle size distributions of high silica chabazite (Si/Al=100) zeolites between 0.3 and 4.5μm is described. The chabzite zeolite crystallization and crystal growth have been monitored using XRD, SEM and DLS. Hydrothermal treatment parameters such as time, temperature and agitation and gel composition parameters such as amounts of water and structure directing agent (SDA) have been correlated with chabazite zeolite crystal size, crystal shape, synthesis yield and crystallinity. From this data a chabazite zeolite formation and crystal growth mechanism based on experimental studies and previous studies has been proposed. It was also found that large aggregates formed in the chabazite zeolite gel before any hydrothermal treatment (1μm large when using zeolite gel with composition 1Al 2 O 3 :100SiO 2 :60TMAdaOH:3100H 2 O). The size controlling parameter and size controlling synthesis step of the chabazite zeolite (below 1μm) has been identified as the primary fractal aggregation of the silicium/aluminium/SDA species.