The objective of this study is to investigate the saturated flow boiling heat transfer of deionized water in a microchannel with nanostructured surface. In this study, to improve the performance of the saturated flow boiling process in the microchannel by using the deposition of nanoparticles on the inner surface of the microchannel, the surface properties such as wettability and surface roughness have been changed. Experiments were performed in a microchannel with an internal diameter of 1.07 mm and a length of 20 cm with de-ionized (DI) water. Experiments were performed under the conditions of mass flux of 493-887 kg/m2 .s and heat flux of 47-227 kW/m2 in the study of two-phase heat transfer. The effect of parameters such as heat flux on the wall as well as the mass flux of the flow on the heat transfer coefficient and also the critical heat flux, which are important parameters in the process of flow boiling, were investigated. In order to prepare the nanofluid, silica nanoparticles were synthesized in a base fluid (methanol) in a single step. The results of DLS test showed the size distribution of synthesized nanoparticles with sizes of 33.7, 64.6 and 89.2 nm. The synthesized silica particles were then dispersed in the main base fluid of deionized water at concentrations of 0.005, 0.01 and 0.05% by volume. In bare surface microchannels with two mass fluxes higher than 684 kg/m2 .s and 887, the dominant mechanism in the channel was nucleate boiling because the effect of two-phase heat transfer coefficient was independent of mass flux and dependent on heat flux and with increasing heat flux it was reduced due to obstruction of the channel with bubbles and local drying. In bare surface microchannel in mass flux of 493 kg/m2 .s the heat transfer coefficient was independent on heat flux so the dominant boiling mechanism was forced convective boiling. The inner surface of microchannel was modified by depositing SiO2 nanoparticles during 80 flow boiling of nanofluid with different sizes and concentrations. An increase of about 32% in the critical heat flux for a mass flux of 493 kg/m2 .s and a nanostructured nanofluid surface with a particle size of 33 nm and a concentration of 0.05% by volume relative to the bare surface and an increase of about 22% for the mass flux 684kg/m2 .s and a particle size of 33 nm and a concentration of 0.05% by volume relative to the bare surface, also mentioned in the two mass fluxes and a concentration of 0.05% by volume of nanofluid with increasing particle size on the nanostructured surface increased critical heat flux. This increase in heat flux could be due to an increase in active nucleate sites and a greater wettability effect at the nanostructured surface with greater roughness than at the bare surface. Keywords: Saturated flow boiling, nanostructure, heat transfer coefficient, nanoparticle synthesis