The award, presented by Budweiser, went to Beltre on Tuesday, two days after he finished up his month with a .337 batting average and a 1.105 OPS in 26 games. He led the league with 71 total bases and a .724 slugging percentage, and finished second with 11 home runs.
The 33-year-old now has won a monthly award for the third time, and is the fourth AL player to take it in consecutive Septembers. The last to do so was the Indians' Albert Belle in 1998-99.
Beltre's big month helped the Rangers clinch a postseason berth and push their magic number for a third straight division title to two as they enter play on Tuesday. He smacked three doubles and a triple, racked up 19 RBIs and scored 19 runs, while not making an error in 54 fielding chances.
Beltre's September contained a trio of three-hit games and a streak of five homers in six days to begin the month. The 15-year-veteran also came through with several key hits, including a game-tying two-run shot and a walk-off single against the A's on Sept. 24. Beltre tied for second in the league with four game-winning RBIs.
Beltre started Tuesday ranked second in the AL with 334 total bases, fourth with a .319 batting average and .560 slugging percentage, sixth with 36 homers and ninth with 101 RBIs.
Andrew Simon is a contributor to MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.