Abstract—The steady mixed convection boundary layer flow of viscoelastic nanofluid past a horizontal circular cylinder taking into account the thermal convective boundary condition is investigated numerically. The nanofluid model use involves the Tiwari and Das model. The resulting system of nonlinear partial differential equations is solved numerically using an efficient implicit finite-difference scheme known as the Keller-box method. Effect of the various parameters, namely, the mixed convection parameter, the nanoparticles volume fraction, viscoelastic parameter and the conjugate parameter on the dimensionless velocity, temperature, skin friction, as well as wall temperature have been presented graphically and discussed. It is found that both skin friction and wall temperature decreases for the increase in the viscoelastic parameter. On the other hand, increasing conjugate parameter leads to the increase of the temperature and velocity profiles. For fixed nanoparticles volume fraction, as the value of the mixed convection parameter increases, the magnitude of both the skin friction coefficient and wall temperature also increases.