They have each paid the $2,000 fee and will be voted on by members of a transitional parliament set up in neighbouring Kenya.
Somalia has been without a functioning central government since 1991, since when rival warlords have battled for control of territory.
Many previous attempts to bring peace to Somalia have failed.
But some say that these talks will succeed because it is backed by all of Somalia's neighbours, and by the donor community.
Correspondents say that of the 27 candidates, three are the favourites:
- Abdulkassim Salat Hassan, who led the previous transitional national government;
- Abdullahi Yusuf, leader of the autonomous Somali region of Puntland;
- Abdullahi Adow, a former ambassador to the US and the man who came second to Mr Salat in the last presidential vote.
The 10 October election is the culmination of a 21-month process, to set up a new government in Somalia.
All the major warlords are represented at the talks in Kenya.
Seats in the parliament were distributed between the rival clans and factions.
The only major absentee is the government of the self-declared republic of Somaliland.
Posted on Tuesday 5th October at 10:17:09