The aim of this work is to study the effect non-uniform single and double slot suction (injection) on an unsteady mixed convection boundary layer flow over a vertical wedge with chemical reaction and heat generation or absorption. The unsteadiness is caused by the time dependent free stream velocity varying arbitrarily with time. Non-similar solutions are obtained by solving the coupled non-linear partial differential equations using the quasi-linearization technique in combination with an implicit finite-difference scheme and numerical computations are carried out for different values of dimensionless parameters to display the effects of non-uniform single and double slot suction (injection) along with chemical reaction and heat generation or absorption. Results indicate that the skin friction, heat and mass transfer coefficients increase with non-uniform slot suction but the effect of non-uniform slot injection is just the opposite. As the slot moves in downstream direction, the skin friction, heat and mass transfer coefficients decrease by non-uniform slot suction whereas non-uniform slot injection has the reverse effect. (C) 2013 Elsevier Ltd. All rights reserved.