Cadbury hopes to take a stronger hold on the expanding Japanese confectionery market thought the acquisition.
The company made the announcement on 20 July.
The company revealed it was making the bid for Sansei last month.
Back then company's chief executive officer Todd Stitzer said the takeover would "further strengthen our presence in Japan, where we have gained significant gum market share since the Adams acquisition".
Cadbury claims to hold the number two position within the £1bn (€1.5bn) Japanese gum market, worth an 18 per cent share through its brands Recaldent and Clorets.
The major boost to its business in the country followed Cadbury's acquisition in 2002 of US-based confectionery group Adams.
Sansei Foods sells sugarfree functional candy in Japan under the brands Teicalo and Xylicrystal.
The company held a 4 per cent share of the Japanese candy market in 2006, said Cadbury Schweppes.
Cadbury put the bid in for the company's shares last month, and needed at least 66.67 per cent of the shares for the offer to be valid.
The company said last week that it would purchase 96.08 per cent of Sansei Foods for £55m (€89m).
Following the purchase, Cadbury will "take procedures prescribed under Japanese law" to purchase the remaining shares, the company stated.
"Sansei's sugarfree high functionality products are complementary to Halls, and we see strong opportunities to develop them further in the Japanese market and potentially elsewhere," said Stitzer.
This move into emerging markets follows Cadbury's acquisitions in the Turkish gum market and of Romania's second largest confectionery company.
The company also announced restructuring plans last month to reduce its cost base and simplify the business, in order to focus on bigger initiatives.
Cadbury recently announced its plans to separate its confectionery and Americas Beverage business as well as the sale of non-core businesses in Australia, Italy and Canada to raise over £45m (€66.4m) towards its 2007 disposal target.