Abstarct: Today, Due to the rapidly increasing use of microfluidic devices (including sudden expansion micro-channel) in various applications, investigation of the flow and heat transfer in sudden expention micro channel, becomes an important problem. In this study numerical investigation of the flow for the copper-water Nano-fluid inside the sudden expansion micro-channel are developed by using of Eulerian–Eulerian two-phase model. In contrast of other models which do not consider the temperature and velocity difference between phases, in this model relative velocity and temperature between phases and volumetric distributing of nano-particles are participated and hence, this model becomes more efficient than single-phase model. In this study, the influence of volumetric distribution of solid particles, expansion ratio of channel, particle diameter and also the injection and suction of nanofluid from vertical walls on the bifurcation phenomena are studied and the effects of the nano-fluid injection and suction from walls on the heat transfer in sudden expansion micro-channel with isotherm walls are analysed. By solving the flow and heat transfer of nanofluids by the Eulerian-Eulerian two phase model, observed that the use of nanofluids lead zoan increase in the critical Reynolds number in comparison to the pure watter. For example, adding 3 volumetric percentage of the copper nanoparticles in water, the critical Reynolds number is increased from 110 to 265. By reducing the expansion coefficient, the critical Reynolds number is also increased. The effect of particle size on the flow is also investigated to show the advantage of this model over other models. In single-phase model, the effects of particle size is not included in the physic of problem, but in the present two phase model the influences of particle size are added. The flow and heat transfer under the influence of injection and suction of nano fluid were investigated by considering the expansion ratio 1: 3 as well as particle diameter which equals to 100 nm. This study showed that the injection increases the critical Reynolds and the suction decreases it. For example, suction with 2% of inlet velocity for 4% copper-water nanofluid decreases the critical Reynolds from 336 to 307. Also, it is showed that the injection and the suction improved heat transfer and increased average Nusselt number, but in injection, the results are so dependent on the temperature of nanofluid which is injected. In the other word, heat transfer reduced when injection temperature is the same as the wall temperature.