When an emulsion is shared, its drops deform and if the intensity of the applied shear is large enough, they break into several droplets. The present experimental work focuses on fragmentation of emulsions in simple shear flow. The influence of the following physicochemical parameters are determined and analysed: shear time, capillary number, flow history, emulsion polydispersity, shear rate, viscous stress, viscosity ratio of the internal and external phases and rheological behaviour of the emulsion. These different studies reveal that the fragmentation of a polydisperse emulsion leads quasi instantaneously to a monodisperse one when the shear flow is intense enough and the initial size of the droplets much larger than the final one.