This paper presents the detailed numerical investigation on the unsteady conjugate mass transfer from a spherical drop immersed in a simple extensional flow. By making use of the known Stokes velocity field at small Reynolds numbers, a finite difference method with the control volume formulation is adopted to solve the convection-diffusion transport equations. The interactive effects of Peclet number, viscosity ratio, diffusivity ratio and distribution coefficient, as well as flow direction on the conjugate transport process are examined in terms of numerical simulation. Simulation results show that the conjugate mass transport is significantly influenced by these four parameters and it approaches some limit cases if viscosity ratio, diffusivity ratio and distribution coefficient become far larger or less than unity. The flow direction, no matter uniaxial extensional or biaxial extensional flow, has no influence on the total transport rate but affects a lot the distribution of solute concentration. (C) 2012 Elsevier Ltd. All rights reserved.