This study quantitatively analyzes the impact of Pix adoption on the pricing of average merchant discount rates (MDR) charged to merchants in the Brazilian acquiring market, focusing on credit and debit functions. The introduction of Pix by the Central Bank of Brazil in November 2020 represented a structural shift in the Brazilian payment system, leading to changes in consumer and merchant behavior. To investigate the effects of Pix on MDR, an econometric model was built using multiple linear regression with quarterly data from 2011 to 2024. The model incorporates control variables for events relevant to the acquiring market during the period, such as the COVID-19 pandemic and the regulation imposing a cap on debit card interchange fees (TIC), in addition to seasonal variables and the basic interest rate (SELIC).