In the late Edo period, the Mitsuis were the richest and most eminent family in Japan, their business being thoroughly encouraged by the shogunal government of the time.

[2] He subsequently started a money exchange in 1683, with a new system for inter-city loans: he extended the family business by opening an outlet in Osaka, and was appointed official purveyor of dry goods to the Tokugawa shogunate in 1687.

Today the Mitsui Group counts dozens of multinational companies in fields such as trade, banking, shipping, construction, mining, oil and gas, insurance, chemicals and real estate development.

The main branches are: As part of the Japanese plans for the exploitation of China, during the 1930s and 1940s the subsidiary tobacco industry of Mitsui zaibatsu had started production of special "Golden Bat" cigarettes using the then-popular in the Far East trademark.

In the mouthpiece of each cigarette a small dose of opium was concealed, and by this subterfuge millions of unsuspecting consumers became drug addicted simultaneously creating huge profits.

The mastermind of the plan, Doihara, was prosecuted and convicted for war crimes before the International Military Tribunal for the Far East, sentenced to death in "pursued a systematic policy of weakening the native inhabitants' will to resist ... by directly and indirectly encouraging the increased production and importation of opium and other narcotics and by promoting the sale and consumption of such drugs among such people";[4] but no actions ever took place against the company which profited from their production.