The software will now not be available until January 2007. Microsoft had previously annouced the second half of this year as the timeframe for launch.
Microsoft plans to launch a product for corporate customers in November and then roll out Windows Vista for consumers after the Christmas shopping season Microsoft platforms and services co-president Jim Allchin said in a conference call.
Vista is the first major overhaul of Windows since Microsoft rolled out Windows XP nearly five years ago.
Microsoft said Vista had been delayed because it wanted to improve overall quality, particularly in security, and that PC makers didn't want the operating system introduced in the middle of Christmas sales, because a new version would create instability in the market.