Around 3,400 weapons used by Maoist fighters in the war against the central government from 1996-2006 had been stored in containers since the end of hostilities.
The Maoists, who turned to mainstream politics and won elections in 2008, had pledged to hand over the weapons after Baburam Bhattarai, himself a Maoist, was elected as prime minister on Sunday.
Disarmament and integration of the Maoists' 19,000 former fighters has been a major obstacle to post-war reform in Nepal, with political parties frequently stuck in debilitating deadlock.
"Our party has handed over the keys" of the containers to a special committee, Chandra Prakash Khanal, a former commander of fighters, told AFP.
The United States embassy in Kathmandu said the decision "signals the commitment of the Maoists to continue moving forward to complete the peace process."
The fate of the 19,000 former fighters remained unclear, with the Nepalese military and main opposition party resisting plans to mould them into the existing national army.
Copyright AFP (Agence France-Presse), 2011