Colloidal GaN nanoparticles were synthesized in distilled water by pulsed laser ablation (PLA) method. Optical and structural analysis were performed on samples generated under different laser fluence by using ultraviolet -visible (UV-vis) absorption spectrophotometer, X-ray diffractometer (XRD) and Tunneling Electron Microscope (TEM) technique. The mean size and size distribution of the nanopartides were investigated using image processing technique of collected TEM images, in addition to XRD patterns. It is shown that laser fluence has a significant effect on nanoparticles size properties. Also, it is proven that the ablation process affects the nanoparticles size and size distribution. The results show that higher laser fluence produces larger mean size of nanoparticles with a broader size distribution. (C) 2017 Elsevier B.V. All rights reserved.