This study analyzes the effect of Ramadan on the market index (Borsa Istanbul-BIST 100) and 23 BIST Sectoral Indices in Borsa Istanbul over the period between January 1997 and December 2015. According to the analysis, the average returns of tourism, service, transportation, electricity, and chemical industries are higher than the market index during the Ramadan period. Moreover, according to regression analysis results, Ramadan has a statistically positive effect on 5 sectors (BIST Transportation, BIST Non-Material Mineral Products, BIST Investment Trust, BIST Electricity, and BIST Chemicals). Also, this study divides the Ramadan days into 3 periods, where the first period comprises the first 10 days of Ramadan, the second period covers the next 10 days, and the final period involves the last 10 days. The first ten days of Ramadan, for most of the indices, have both positive and statistically significant returns.