This paper deals with the development of the morphology in polyethylene glycol (PEG) and polyamide 66 (PA66) immiscible blends exhibiting an extremely low viscosity ratio (eta(PEG)/eta(PA66) = 3-4 x 10(-5)). These materials were obtained by melt mixing, under different operating conditions, using a twin-screw batch-type DSM mini-extruder. Scanning electron microscopy, followed by quantitative image analysis was used to determine PEG particles size distribution (PSD) as a function of blends composition and screw rotation speed. Experiments carried out with two mixing time (5 and 10 min) showed no significant difference of PSD. So, to avoid thermal degradation of the products, the mixing time was set up at 5 min for all experiments. The influence of PEG concentration and screw rotation speed on PSD appeared to be similar to that obtained in a previous study for the same blends elaborated in a Haake internal mixer. The results clearly showed that the average particle diameters decreased as screw rotation speed increased and as PEG concentration decreased. However, this decrease is less important using the twin-screw batch-type mini-extruder with which the particle sizes are smaller. The particles sizes were then correlated to blend composition, shear rate and viscosity ratio owing to an extension of Serpe's model. The unknown parameters of the corresponding model were estimated on the basis of experimental data. This enabled then to predict with a good precision the influence of the process operating conditions on the morphology of the dispersed phase. (C) 2009 Elsevier Ltd. All rights reserved.