About 300 mock trials were held ahead of Monday's case
Japan has opened its first jury trial for more than 60 years, after making changes to a legal system which has often been criticised as unfair.
Six jurors are working with three judges to decide a verdict in the case of 72-year-old Katsuyoshi Fujii, who has been charged with murder.
Until now Japanese trials have been decided by a panel of judges.
Critics say the old system was too slow, lacked transparency and was out of touch.
But some legal experts remain concerned that randomly selected members of the public are not fit to decide the outcome of serious crime cases, especially those involving a possible death penalty.
In the past the justice system in Japan has been notoriously secretive, with a system of judge-only trials and private police interrogations.
Criminal trials currently have a 99% conviction rate, and there are increasing concerns that the system of judge-only trials and private police interrogations leads to false confessions and the conviction of innocent people.
The jurors at Tokyo District Court have four days to decide the verdict and, if guilty, the sentence for Katsuyoshi Fujii.
He is charged with the fatal stabbing of a 66-year-old neighbour in May.
At least one of three professional judges presiding over the trial must agree with the jury's decision for it to stand.
"We hope to achieve a justice system that is speedier, more accessible and reliable," Justice Minister Eisuke Mori told reporters.
"With the change, trials will become more democratic," he added.
In all there are set to be about 2,000 to 3,000 jury trials a year, all of them for serious crimes such as murder and rape.
Japan has the death penalty, but this is only usually given for multiple murders.
Candidates for jury service will be randomly selected from eligible voters nationwide.
About 300 mock trials have already been held in preparation for the new system.
Japan first launched a jury system in 1928, but dropped it in 1943 during World War II.