The telecommunications industry in Brazil had been through significant changes during the mid-1990's and the beginning of the 21st century, due to a new regulation and the privatization of the state-owned telephony monopolistic operators. These regulatory changes caused a major transformation in this industry's competitive environment and in the recently privatized operators competitive strategies. This dissertation seeks to identify changes in the competitive environment by means of a more detailed analysis of a privatized operator, this company's competitive strategies and performance indicators through a comparison of two distinct periods - before (1996-1998) and after (1999-2003) the privatization. In order to identify the competitive strategies, the selected company was classified under 20 strategic variables, according to Porter's (1980) typology. The research is based on interviews with current and former employees from the selected company, its competitors and the industry's consulting firms. During the period that preceded the privatization process (1996-1998), the company's strategy can not be classified under Porter's (1980) typology due to the monopolistic regime in which the company provided its services, although it was possible to infer that the company's strategy seems closer to a differentiation strategy than other generic strategies. On the other hand, during the period following the privatization (1999-2003), the company positioned itself on a differentiation strategy, although some adopted tactics might diverge from this positioning. In spite of successfully adopting a differentiation strategy, the company's results have decreased, as shown by a comparison of performance indicators from both periods. These poorer results after the new regulation are mainly due to a much more hostile competitive environment than before.