Qihoo 360, launched just two weeks ago, said when people use its new engine to search for a Baidu-related service, its rival "hijacks" the search to take them to its own search home page.
"Every time now users do a search about Baidu, instead of being taken to a particular Baidu Web site, they are re-directed to Baidu's search homepage," Qihoo's chief financial officer Alex Xu told the BBC.
"Let's say if you do a map search, and you get a link to a Baidu map in the search result -- if you click on it, you don't get a map, you get Baidu's search page.
"That's not how a web company is supposed to behave -- you're affecting the users' experience," Xu said.
Qihoo said it's responding by giving search results from other services higher priority in its results than Baidu's.
Baidu, which has 80 percent of the Chinese search market, has not faced any real competition since Google shut down its Chinese search site at Google.cn.