The article discusses about the relation between constitutional rigidity and democracy. According to liberal theory, flexible constitutions (or decreasing levels of constitutional rigidity) produces weak democracies. In order to asses that this relation is not aplicable for every case, the research explores the case of Uruguay as an exceptional case: low levels of contitutional rigidity; stable democracy and inexistance of reforms that erodes democracy. Also, the paper discusses about the flaws of stringent amendment rules, exploring two cases: Venezuela under 1961 constitution and Chile under the rule of 1980 constitution. The case analisis shows that flexible constitutions not necesarilly leads to weak democracies. On the other hand, the potential problem of stringent amendment rules is the lack of response to the demands from the environment.