Schmidt, speaking at a Washington think-tank, said he was "sympathetic" to the arguments of law enforcement and intelligence agencies seeking to thwart crime and terrorism, but that it is not feasible to create access only for "the good guys."
"We don't know how to build a trap door in these systems which is only available to the good guys," the Google chief said at a forum at the American Enterprise Institute.
"If we put a trap door in our system, first, we would have to disclose it because people would find out anyway. And second, some evil person in addition to the good guys would figure out a way to get in."
Schmidt's comments come after the heads of the FBI and National Security Agency complained that encryption on devices being implemented by Google, Apple and others is hurting their ability to track down criminals and terrorists.
The Google chief said however that allowing special access would be tantamount to a system allowing the government "to watch what everyone is doing in order to figure out who the bad guys are."
"We've taken a very tough line in the industry over this issue and I think we will win this one, at least in America," Schmidt said.