OptionsXpress stock jumped $2.51, 16.4 percent, to $17.84 in pre-market trading. Schwab shares added 9 cents to $17.65.
The discount broker said OptionsXpress shareholders will receive 1.02 shares of Schwab stock for each share of OptionsXpress share.
Based on Schwab's closing price on Friday of $17.91, the transaction is valued at $1 billion.
OptionsXpress Holdings Inc., based in Chicago, provides brokerage services for equity options and futures trading. At the end of February, the company had 385,200 client accounts and $8.1 billion in client assets.
Charles Schwab Corp. has $1.6 trillion in client assets at the end of the same period.
The deal is expected to close in the third quarter.