From August 1 to the end of the month, Muslims around the world will be fasting from dawn to sunset and praying.
Open Door USA has produced a Ramadan calendar suggesting a different prayer focus for each day during Ramadan, such as forbearance, faithfulness, gentleness and self-control.
"Ramadan is a time when Christians are especially isolated in some Muslim-dominated countries," said Dr Carl Moeller, President and Chief Executive of Open Doors USA.
"This is why it is so important for us to unite in prayer with persecuted Christians throughout the world.
"I urge you to use the Open Doors resources to pray with our brothers and sisters."
Largely Muslim countries dominate the top 10 world's worst persecutors of Christians, as listed in this year's Open Doors World Watch List.
The 10 worst persecutors included eight Muslim-dominated societies, among them Iran, Afghanistan, Saudi Arabia and Somalia.
There are difficulties for Christians even in countries considered more moderate, such as Egypt, where Christians have been killed in church attacks by extremists.
Open Doors warned that the observance of Ramadan could "increase pressure" on believers in Muslim-majority countries.
The end of Ramadan will be followed a fortnight later by the tenth anniversary of the 9/11 terrorist attacks.
Michele Miller, Director of Open Doors Prayer Ministries, said it was vital that the church pray for both Christians and Muslims during the 9/11 anniversary.
"Prayer has changed the hearts of millions, so it is also important to pray past the month of Ramadan," she said.
To download the prayer calendar, visit www.opendoorsusa.org/pray/Ramadan