Nike has until next week to match Adidas' offer.
Nike, whose contract with Harden recently expired, reportedly has until the end of next week to match the offer.
"We've invited James Harden to join Adidas," said Adidas spokesman Michael Ehrlich in a statement. "We're a brand of creators and he truly embodies what that means with his approach to the game, his look and his style on and off the court."
Harden had the best season of his career in 2014-15, averaging 27.4 points, 7.0 assists and 5.7 blocks in 36.8 minutes per game. He led the Rockets to the Western Conference Finals, where the team fell to the Golden State Warriors in five games.
In March, Adidas decided not to bid for a new apparel rights deal in the NBA. One month later, Nike signed a deal to feature their swoosh on all team uniforms. Nike's deal will take effect when Adidas' contract expires at the end of the 2016-17 season.
Adidas recently fell to third in U.S. apparel brand sales after being surpassed by Under Armour, which is endorsed by 2015 NBA MVP Stephen Curry.
Harden signed a five-year extension worth $80 million with the Rockets in 2012 and finished second in MVP voting at the end of last season.
Data curated by pointafter.com
- Christopher Chavez