Acuna and Ohtani were presented with the awards on Monday by the Baseball Writers Association of America.
Acuna received 27 of 30 first-place votes for the award. Ohtani received 25 first-place votes. Washington Nationals star Juan Soto finished in second place for the National League honor while New York Yankees star Miguel Andujar finished in second place for the American League award.
Ohtani, 24, hit .285 with 22 home runs, 61 RBIs and 10 stolen bases in 104 games this season for the Angels. He also posted a 3.31 ERA and a 4-2 record in 10 starts. Acuna, 20, hit .293 with 26 home runs, 64 RBIs and 16 stolen bases in 111 games for the Braves.
"I'm really honored," Ohtani said during a conference call with reporters. "It's really unbelievable that I was able to win this award, and how I was able to win it at such a high level of competition in Major League Baseball. I'm really proud of this award."
The BBWA announces its Managers of the Year on Tuesday, Cy Young Award winners on Wednesday and Most Valuable Players on Thursday.
"I'm just flattered. I'm so honored to receive this award," Acuna told MLB.com. "My career is just beginning. There are just so many things I need to do to become a better player. I like to take in all the advice from other people to improve every year, to become a better person and a better player."