The work here presented is the development of a model for the measurement and evaluation of the usability of web sites of the Colombian virtual bank; the methodology used was that of a heuristic evaluation by experts, which takes into account the inherent objectives of the domain and the necessities of the navigators, in addition to their profile. There are several methodologies to evaluate the usability of web sites, such as: iterative revision, ClickStream, on-line questionnaire, heuristic evaluation by experts, users’ test, cognitive walkthrough, pluralistic walkthrough, interviews with users, thinking aloud, card sorting, scientific method, ethnographic study, SUMI - QUIS, ESPRIT MUSIC, evaluation of the intercultural usability, evaluation of the accessibility, studies of documentation, and predictive system performance models. The heuristic evaluation by experts was selected due to several reasons: it is based on the evaluators’ expertise on the subject; it is an informal, easy-toapply methodology; it has low cost and concrete results; it is accurate and reliable in terms of web site usability. Evaluation results can be used to make a report that allows banks to know what is happening to users who make transactions through their Internet pages, whether the web sites efficiently satisfy their needs and objectives, and also if each site provides them with accessibility, trustworthiness and functionality.