Half of the 242 seats in the upper legislative chamber are up for grabs, in what is expected to be the last national election for three years.
With approval ratings well over 60 percent seven months after he won the premiership in a general election, a win for the hawkish premier's ruling bloc is all but assured.
Control of both chambers will remove political obstacles to Abe's agenda.
Supporters say that will give him free reign to force unpopular changes on Japan's long under-performing economy.
More From This Section
The reforms are the third instalment of an economic policy plan dubbed "Abenomics" that has already seen a slew of government spending and a flood of easy money from the central bank.
Those moves pushed the value of the yen down and sent the stock market soaring, bringing cheer to some sectors of corporate Japan.
They fear this will mean a loosening of Japan's constitutional commitment to pacifism, a boosting of the military and a more strident tone in already-strained relations with China and South Korea, both of which have territorial disputes with Tokyo.
Whatever Abe's intentions, the predicted swing towards his Liberal Democratic Party and their junior coalition allies could give Japan its first long-term prime minister since Junichiro Koizumi, who ruled for the first half of last decade.