The organisation now feels the only way to get a true picture of what is going on in the nation's classrooms is to drop in by surprise.
New Ofsted chief Sir Michael Wilshaw said: "We are introducing no-notice inspections for all schools from this September, not just those that are causing concern.
"There are a number of reasons. First of all it's a logical progression from the situation years ago when there was a year's notice, then it was two weeks, and in 2005 it went to two days.
"It provides an opportunity for inspectors to do what's really important - going in and inspecting quality, particularly teaching."
Under the new guidelines, inspectors will no longer have to spend time going through documentation before visits.
"We want to make sure that the public views the process as something that's rigorous and robust and there's no question that schools are not going to follow the rules," Sir Michael said
Earlier this week it was claimed that disruptive pupils were being bribed up to £100 each to stay away from lessons during Ofsted inspections.
Despite having good attendance records, poorly-behaved students are being paid to truant to prevent their schools getting bad ratings, it was alleged.