This study investigates whether religious belief creates stock market return seasonality, focusing on the Muslim holy month “Ramadan". We use long-term data from 12 stock markets in countries with a high Muslim majority. Using a structural time-series model that takes into account a “trend component" and a stochastic “seasonal component”, we find no significant evidence of Ramadan return seasonality for the 12 stock markets over the long-term. This result suggests that there is no trend component for Ramadan effect and that Ramadan returns seasonality vanish in the long-term.