This research aimed to directly evaluate the impact of the accounting regulatory flexibility movement on the comparability of financial reports. The country chosen for the analysis was Brazil, because it was one of the few countries in the world where a process of regulatory change from a completely rule-based standard with a strong link to tax accounting (Lopes, 2011) to a principle-based standard with greater need for decision by managers who prepare the financial reports took place. To measure comparability, the accounting function similarity model developed by DeFranco, Kothari and Verdi (2011) was used. The companies analyzed were all listed ones with full data for the period concerned having, at least, a pair company within the same economic activity sector. To obtain the research results, we adopted a panel data model where the years 2005 to 2012 were compared to the year 2004. The results obtained prove that, on average, there was no significant decrease in the comparability level within country during the regulatory transition period in Brazil. On the contrary, there was an increase in genuine comparability in the year 2012 when compared to 2004. In the model adjusted by stepwise, the years 2011 and 2012 had a significantly higher average comparability when compared to 2004. The results found corroborate other researches addressing the quality of accounting information (Collins, Pasewark, & Riley, 2012; Psaros & Trotman, 2004; Agoglia, Doupnik, & Tsakumis, 2011) and prove the superiority of the principle-based standard also over the comparability of financial reports. The main conclusion of this research is that increasing manager's discretionary power through flexibility of accounting standards does not decrease the comparability of financial reports.