This　paper　presents　a　numerical　study　of　natural　convective　heat　transfer　of　copper-water　nanofluid　in　a　square　enclosure　where　the　temperature　of　the　left　vertical　sidewall　is　sinusoidally　oscillated　with　a　constant　average　temperature,　the　right　sidewall　is　cooled　at　a　relatively　low　temperature,　and　the　other　walls　are　kept　adiabatic.　The　influence　of　pertinent　parameters　such　as　Rayleigh　number,　solid　volume　fraction　of　copper　nanoparticles,　and　dimensionless　time　period　on　the　heat　transfer　characteristics　is　studied.　The　results　show　that　the　heat　transfer　rate　increases　using　copper　nanoparticles.