The group said it was offering Ciba shareholders €30 per share which was 32 percent more than the closing price Friday and 60 percent more than the average over the last 30 days before the announcement of the takeover bid.
Ciba's board of directors backs the deal, BASF said in a statement, adding that it would formally make its offer on October 1.
Ciba shares soared on the Swiss stock market Monday after BASF's statement. By 10 am the stock had gained 28.95 percent to 49 Swiss francs while the Swiss Leader Index slid 2.38 percent.
BASF had said recently it was interested in new acquisitions, particularly in the specialized chemicals sector.
"In the current consolidation phase in the chemicals industry, the acquisition of Ciba offers clear advantages in terms of global competition," BASF head Jürgen Hambrecht said in a statement.