An analysis is performed to investigate the effects of Joule heating and thermal diffusion on unsteady, viscous, incompressible, electrically conducting MHD heat and mass transfer free convection Casson fluid flow past an oscillating semi-infinite vertical moving porous plate in the presence of heat source/sink and an applied transverse magnetic field. Initially it is assumed that the plate and surrounding fluid at the same temperature and concentration at all the points in stationary condition in the entire flow region. Thereafter a constant temperature is given to the plate hence the buoyancy effect is supporting the fluid to move in upward direction and is assumed that gravity is the only force which acts against to the flow direction. The governing flow is modeled in the form of partial differential equations with initial and boundary conditions. With suitable nondimensional quantities the governing non-linear partial differential equations obtained in dimensionless form, which are solved numerically with finite difference scheme. Numerical results for non-dimensional velocity, temperature and concentration as well as the skin-friciton, the rate of heat transfer and the rate of mass transfer studied for different physical parameters. The results show that the solutal boundary layer thickness of the fluid enhances with the increase of Prandtl number and the temperature is increased by an increase in the heat source by the fluid. The central reason behind this effect is that the heat source causes an increase in the kinetic energy as well as thermal energy of the fluid. The momentum and thermal boundary layers get thinner in case of heat source fluids. © 2017, Global Digital Central. All rights reserved.