The infrared cloud amount with cloud tops above 180 hPa from the International Satellite Cloud Climatology Project D1 cloud product and the Tropical Rainfall Measurement Mission 3B42 precipitation product are employed to study the impact of the Madden-Julian Oscillation (MJO) on the diurnal cycle of tropical deep convective cloud amount (DCC). Our analysis demonstrates that the diurnal cycle of tropical DCC is enhanced over both land and water during the convectively active phase of the MJO, while it is reduced during the convectively suppressed phase of the MJO. However, the diurnal phase of DCC is not significantly affected by the MJO. The analysis also indicates that the MJO modulation of the diurnal amplitude is much larger over the eastern Indian Ocean (around 50% of the mean diurnal amplitude) than over the western Pacific and the Maritime Continents (around 20% of the mean diurnal amplitude).