This paper deals with the development of an inventory model for Weibull deteriorating items in quadratic demand market when delay in payments is allowed to the retailer to settle the account against the purchases made by him. Shortages are not allowed. In this paper we have considered two cases; those are for the case payment within the permissible time and for payment after the expiry of permissible time. Numerical examples are provided to illustrate our results. Sensitivity analysis has been carried out to analyze the changes in the optimal solution with respect to deterioration rate of units in inventory and the rate of change of demand.