The 31 cabinet members announced by Ali Mohamed Gedi on Monday replace the previous cabinet dissolved by the president, Abdullahi Yusuf, on August 7 who described the executive as bloated and ineffective.
The Somali government has been paralysed for nearly two years by infighting and more recently by pressure from Islamist factions.
It was not immediately clear whether Gedi included any Islamists or Islamist allies in the new, smaller cabinet.
After dissolving the cabinet, Yusuf had ordered Gedi to name a smaller one that would be reviewed on its performance in three months. Gedi missed Yusuf's seven-day deadline by a week.
Monday's announcement came after Gedi consulted with Yusuf, Sharif Hassan Sheikh Adan, the parliamentary speaker, and lawmakers and traditional elders.
"After the meetings, the prime minister re-formed his government," a government spokesman, Abdirahman Dinari, told a news conference in the town of Baidoa, where the government is temporarily based.
Gedi's reshuffle was part of a deal brokered by Ethiopia, after he narrowly survived a no-confidence vote on July 30 and saw half his cabinet resign in frustration over his reluctance to negotiate with the Islamists.
The Islamists' rise is the single biggest threat to the interim government, formed at peace talks in Kenya in 2004.
The government was just the latest attempt to provide central authority and stability to a country in political anarchy since the former dictator, Mohamed Siad Barre, was overthrown in 1991.
The Islamists emerged as a political and military force in June after they defeated US-backed commanders and seized control of Mogadishu and strategic areas around it.
Some members of parliament saw the new cabinet as an opportunity to bring the Islamists, who are mostly from Gedi's Hawiye clan, into government.