Abstract- This paper presents the results of a numerical study on the natural convection in a right triangular enclosure filled with a water- Cu nanofluid in presence of a constant magnetic field. A heat source embedded on the bottom wall of enclosure, the inclined wall is cold and the other walls are adiabatic. Discretization of the governing equations are achieved through a finite volume method and solved with SIMPLE algorithm. The effects of parameters such as the Reyleigh number, the solid volume fraction, the Hartman number, length and location of heat source on flow and temperature fields and the heat transfer rate have been examined. The results show that increasing of Hartman number caused decreasing velocity of flow and heat transfer. Also, increase in solid volume fraction causes increase in heat transfer but its change in different Reyleigh number and Hartman number is not same. Therefore, the location of heat source in bottom of enclosure affects on the rate of heat transfer from enclosure.