This research presents the concepts of electronic commerce and it searches the comprehension on how usability aspects and information architecture can contribute to an experience centered on the user that will promote a bigger satisfaction and will increase the chances of having an on- line purchase concluded. In order to verify the hypothesis that usability aspects of interface of forms are determinant on successful filling in and conclusion of on-line purchase, some sites as Lojas Americanas, Casa e Vídeo, Ponto Frio and Submarino were selected. Among the methods and techniques used in this work, it is necessary to distinguish focus group, card sorting, usability test and satisfaction questionnaires. Focus group was used in the initial phases of this research to collect information about users` motivations, beliefs and attitudes; in essence: what users have said they have thought. It was used card sorting to understand how users had understood the system, through some exercises by which was possible to verify how they have grouped and labeled the requested information. Thus, this work has searched to capture not what users have said they have thought, but what they have been thinking. Usability tests promoted the observation and analysis on how users have interacted with the system. Hence, it was possible to verify not what users have said or what they have thought, but what they had done. Users` satisfaction questionnaires were administered to collect quantitative data, commentaries and observation about some specific attributes of interaction between users and electronic commerce forms. By the agency of those relational and individual analyses of methods and techniques results, it was enabled to confirm the hypothesis that usability aspects are important on successful filling in and on the conclusion of on-line purchase. Thus, it was also possible to point out some directives to the elaboration of electronic forms to conclude on-line purchase in the Internet.