The Sylvania 300 is a NASCAR Nextel Cup stock car race held at the New Hampshire International Speedway in Loudon, New Hampshire.

The Sylvania 300 has traditionally held in mid-September, however, the race has been rescheduled once in its history. Originally scheduled to run on September 16, 2001, it was postponed due to the September 11, 2001 attacks. Not wanting to cancel the event outright, NASCAR decided to reschedule the race to the next available date, November 23, 2001, the day after Thanksgiving. This created an interesting challenge for Goodyear, the tire manufacturer, as they were not expecting to run a race in New Hampshire in November, at a much colder time of year than normal, with snow a possibility. They brought a tire that they hoped would be better suited to the cold conditions, and NASCAR scheduled the race for a Friday in order to allow for two available weather dates, but at the time of the race, their concerns were unfounded, the race took place with high temps in the 50s, with live national television coverage being tape-delayed in the West Coast to accommodate NBC's third hour of Today.

The Sylvania 300 also has the distinction of being the only Nextel Cup race outside of Daytona and Talladega to run a restrictor plate race since the adoption of the current 358 cubic inch formula. After Adam Petty's fatal crash in the Busch Series practice in May, and Kenny Irwin, Jr.'s fatal crash in the Cup Series practice in July, NASCAR decided to run restrictor plates, already used for the Whelen Modified Tour races at the circuit, for the 2000 Cup race, then known as the Dura Lube 300 sponsored by Kmart. Adding restrictor plates did have the desired result of slowing down the cars drastically, but at the same time, restricted passing so much that Jeff Burton led all 300 laps. This lack of passing was so uncompetitive, that for Cup cars only, the restrictor plates were gone for the very next race, the 2001 New England 300.

Since 2004, the race has served as the opening round the "Chase for the NEXTEL Cup", a ten-race "playoff" designed among the top ten drivers in the standings of the series following the Chevy Rock and Roll 400 to spur interest in a championship series while NASCAR faces competition from the start of the NFL season and college football, the pennant races and post-season of Major League Baseball and the outset of the NHL and NBA seasons.

It was announced on July 15, 2006 that the title sponsor Sylvania signed an extension until 2012 to be the title sponsor of the race. This most likely will secure the track's September race until 2012.