Particles from Gas Saturated Solution (PGSS) is one of the supercritical fluid techniques for nanoparticles generation. This process has different and unique advantages; producing very fine particles with the same and narrow size distribution, particle size controllability, high purity of particle without solvent residue. Modeling of this process helps the researchers to investigate the effects of important operating and design parameters on the nanoparticles size desi+++++++gn. From available methods for nanoparticles generation by supercritical fluid, Particles from Gas Saturated Solution was chosen for modeling, because this method has some advantages in contrast to other methods. Important advantages with respect to other methods are: (1) this process requires lower pressure compare to Rapid Expansion of Supercritical Solution(RESS), (2) this method has lower consumption of gas compare to Supercritical Anti Solvent(SAS), because in this process there is lower ratio of gas in liquid, (3) this process can generate particles without any solvent residue, and (4) this process has the possibility of nanoparticles generation for encapsulated pharmacicual applications. Main goals of this thesis was to model this process and model validation via comparison with experimental data. Furthermore, the validation model was used to investigate the effect of different design and operating variables on the particle size of the synthesis sized nanoparticles. Moreover, the parametric analysis of nanoparticle size design was carried out at the different operating range of effective variables. In this thesis by comparing results of model with a particular experimental data ( pharmacicual nanoparticles of nifedipine ) the accuracy of model was checked. Based on the input data given to the computer program, the model predicted data had 1-3% error in contrast to experimental results. The other reported models in the literature has higher error than the model of this study. Thus, this model was used to investigate the effect of different parameters such as pre-expansion temperature , pre-expansion pressure , nozzle diameter and heat flux on the average particle diameter and so we can use this model to know effect of dependent parameters to get profiles of thermodynamic profiles of thermodynamic properties along the nozzle and capillary. Dependent on entrance conditions to nozzle, average of particle diameter can be in the range of 20- 23 µm. The obtained narrow particle size distribution is a normal Gaussian curve which coincide with experimental data. Modeling results of Particles from Gas Saturated Solution showed that; increasing the pre-expansion temperature produced smaller particles because temperature is an effective parameter on the growth of particles. The increasing pre-expansion pressure led to the synthesis of smaller particles. Modeling results of PGSS showed that, heat flux of expansion device (nozzle), if driving process to adiabatic path led to smaller particles. The modeling results show that increasing nozzle diameter led to larger particles, so that small diameter of nozzle is appropriate (suitable) design condition. Keywords: modeling, supercritical fluid, nanoparticles, nifedipine, PGSS