The Tigers bumped Oklahoma from the top spot Sunday after winning 47-21 at West Virginia the night before.
The Sooners had been No. 1 since the preseason. They stayed unbeaten with a 38-28 victory at home against Missouri.
LSU received 42 first-place votes from the 60-member media panel and 1,471 points. Oklahoma received 12 first-place votes and 1,422 points.
No. 3 Alabama received 5 first-place votes and No. 4 Boise State had one.
Oklahoma State jumped two spots to No. 5 after winning at Texas A&M.
The Tigers haven't been No. 1 since winning the national championship in 2007. The Tigers held the top ranking for four weeks during the regular season that year.
LSU (4-0) added the victory against West Virginia to wins over Oregon at Dallas Cowboys Stadium and at Mississippi State. All three were ranked at the time the Tigers played them.
"We have a real strong road personality," LSU coach Les Miles said. "I think there's some real confidence for this football team that no matter what the environment is, you know, we can play."
Oklahoma certainly hasn't struggled, with wins against Tulsa, at Florida State and Missouri.
Though Sooners linebacker Travis Lewis sort of predicted the demotion Saturday night after the Missouri game.
"We played like a 25th-, 30th-ranked team," he said. "We are not the No. 1 ranked team in the nation right now."
Losing the top spot in the polls after a victory isn't uncommon. It happened once last season and twice the season before.
For now, the Tigers' resume' has swayed voters.
The schedule doesn't let up much for LSU, though the Tigers do play at home the next two weeks against Kentucky (2-2) and No. 12 Florida (4-0).
No. 6 is Stanford, followed by Wisconsin and Nebraska. The seventh-ranked Badgers will welcome the eight-ranked Cornhuskers to the Big Ten on Saturday in Madison, as Nebraska plays its first game in its new conference.
Oregon is No. 9 and South Carolina is 10th.
No. 11 Virginia Tech hosts No. 13 Clemson in the Atlantic Coast Conference's biggest game of the upcoming. The Tigers moved up eight spots after beating Florida State 35-30 in Death Valley.
The Seminoles slipped 12 spots to No. 23 after its second consecutive loss.
No. 12 Florida hosts Alabama in the SEC's biggest game.
Texas A&M slipped six spots to No. 14 after losing to Oklahoma State.
Baylor and quarterback Robert Griffin III, who has 13 touchdown passes against only 12 incomplete passes this season, is 15th.
No. 16 South Florida is followed by Texas, Arkansas, Michigan and TCU.
The final five were Georgia Tech, West Virginia, which slipped six spots, Florida State, Illinois and Arizona State.
The Sun Devils slipped back into the rankings after snapping an 11-game losing streak to Southern California with a 43-22 victory.
USC was the only team to fall out of the rankings this week.