The business achievement via e-commerce is getting more important at the present time. E-commerce implies several activities. One of the most significant activity is the consummation of negotiations between sellers and buyers with the aim of reaching agreements. In order to automate these activities the intelligent agent software model is applied. In this work, it is proposed the design of a seller agent for negotiating in competitive frameworks, where many seller agents and a buyer agent negotiate products or services based on several properties. In that context, the aim of the seller agent will be to make offers that improve the other ones sent by other sellers and to maximize its profit. The design is based on the application of fuzzy logic and evolutional algorithms.