The outcome was widely expected in elections held after the fatal shooting of prominent ruling LDP member and power broker, former premier Shinzo Abe.
Japan's ruling coalition is projected to have won the most votes in an election held just two days after the assassination of former prime minister Shinzo Abe, national broadcaster NHK has said.
The ex-premier's ruling Liberal Democratic Party (LDP) and its coalition partner Komeito are expected to claim between 69 and 83 of the 125 upper house seats up for grabs in Sunday's elections.
Even before Abe's murder, the LDP and Komeito were expected to cement their majority, though the final number of seats will be scrutinised for signs of whether the attack bolstered support for them.
Prime Minister Fumio Kishida had insisted the election proceed despite the assassination, saying "we must never allow violence to suppress speech".
With little violent crime, and tough gun laws, security at Japanese campaign events can be relaxed, though in the wake of Abe's murder, measures were beefed up for Kishida's remaining appearances.
READ MORE: Japan goes to polls in shadow of ex-PM Abe assassination
Assassination shocked the world
Abe was gunned down at close range on Friday in the western region of Nara, and died of blood loss at a local hospital. His body was brought to his family home in Tokyo on Saturday.
The assassination rattled the nation and sent shockwaves around the world, prompting an outpouring of sympathy even from nations with which the hawkish Abe had sometimes difficult relations, like China and South Korea.
The man accused of his murder, 41-year-old Tetsuya Yamagami, is in custody and has told investigators he targeted Abe because he believed the politician was linked to an unnamed organisation.
Local media have described the organisation as religious and said Yamagami's family had suffered financial trouble as a result of his mother's donations to the group.
He reportedly visited the western region of Okayama on Thursday with the intent of killing Abe at a different event, but backed out because participants had to submit their names and addresses.
READ MORE: Japan mourns as body of assassinated ex-PM Abe returns to Tokyo