A weak onlinear analysis of double diffusive convection in an electrically conducting viscoelastic fluid layer heated from below, has been performed for the range of viscoelastic parameters where oscillatory mode exists. A uniform magnetic field has been applied vertically. Employing complex non-autonomous Ginzburg-Landau equation, the effects of various parameters on double diffusive convection is investigated. Weak nonlinear analysis reveals that the values of viscoelastic parameters have significant effect on the instability. The present study is to investigate the effect of time periodic gravity field on heat and mass transfer in the presence of external magnetic field, where controlling convection external to the system is important. It is found that the variation of Nusselt, Sherwood numbers with respect to the slow time becomes rapid upon increasing the solutal Rayleigh number Rs, Prandtl number Pr, time relaxation parameter and amplitude of modulation 32 or decreasing on Chandrasekhar number Q, diffusivity ratio Gamma, time retardation parameter epsilon and frequency of modulation a It is found that the applied magnetic field has a stabilizing effect, hence reducing heat and mass transport in the system. Further, modulated gravity field can be used either to delay or enhance the heat and mass transfer in the system. Chaotic convection under gravity modulation has also been investigated using Lorenz model. (C) 2014 Elsevier Ltd. All rights reserved.