Shares of Unilever jumped 8.1%, while Kraft Heinz stock rose 3.1%.
"While Unilever has declined the proposal, we look forward to working to reach an agreement on the terms of a transaction," Kraft Heinz said in the statement.
Kraft brands include Oscar Meyer, Velveeta and Jell-O. Dove, Lipton and Vaseline are among Unilever's brands. Kraft stock is up 17.6% in the past year, Unilever shares are down 1.4% over that period, and the S&P 500 index is up 21.8% in the past 12 months.