The transient behaviors of natural convection heat and mass transfer along a vertical wavy surface subjected to step changes of wall temperature and wall concentration have been investigated numerically by using a simple coordinate transformation to transform the complex wavy surface into a flat plate. An implicit marching finite-difference scheme is employed for the analysis. It is well know that the buoyancy ratio N and Schmidt number Se are the parameters of importance for heat and mass transfer. The wavy geometry is also an important factor for this problem. Numerical results show that the flow field takes more time to reach steady condition for a high amplitude-wavelength ratio a, small buoyancy ratio N, and large Schmidt number Sc. The effects of wavy geometry, buoyancy ratio N and Schmidt number Sc on the transient local skin-friction, local Nusselt number and local Sherwood number have been discussed in detail. (C) 2004 Elsevier Ltd. All rights reserved.