The General Authority of Islamic Affairs and Endowment (GAIAE) in the United Arab Emirates said that anyone making such a "hazardous trip" is likely to die for "no righteous reason".
They would therefore be liable to a "punishment similar to that of suicide in the Hereafter", the Khaleej Times reported.
The Fatwa was apparently issued in response to the proposal from the Dutch company Mars One last year to send four people on a one-way journey to the red planet in 2022.
Over 200,000 people have applied to be civilian-astronauts on the Mars One mission. Experts have questioned both the financial and practical viability of the mission.