Iranian President Mahmoud Ahmadinejad has dismissed the oil minister and two other ministers.
The official Iranian news agency says the ministers of oil, social welfare and industries and mines were dismissed by the president in order to slim down the government's ministries from 21 to 17.
A shake-up of the department in charge of the world's fifth-biggest oil exporter was expected after some officials said earlier this month that the oil and energy ministries and labour and social welfare ministries would be merged.
No announcement has been made about who will take over any new merged portfolios.
Parliament would have to approve the remit of any new ministry.
Getting approval from parliament, whose speaker Ali Larijani has publicly criticised Mr Ahmadinejad's domestic and economic policies, will not be easy.
Iran's top authority, Ayatollah Ali Khamenei, has a discretion over key ministries, including oil, foreign, intelligence and interior.