Their infection marks the first two confirmed cases of MERS in Iran.
According to the Iranian Ministry of Health, one of the sisters is in critical condition while the other is receiving treatment.
To date, the virus has killed 175 people in neighboring Saudi Arabia.
The MERS coronavirus causes acute respiratory illness. Its symptoms include fever, cough and shortness of breath. The majority of its victims do not survive, according to the U.S. Centers for Disease Control.
It is regarded as a deadlier but less-easily transmitted form of the SARS virus, which began in Asia in 2003 and infected 8,273 people, 744 of whom died.