Tatsujiro Fukazawa was arrested Thursday for allegedly trying to kill his colleague, Teyuaki Harano, with the acid attack in December, CNN reported Friday.
Fukazawa and Harano worked in a laboratory at a company in Tokyo that makes carbon-fiber products.
Police said they suspect Fukazawa had romantic feelings for Harano, though how those feelings translated into the attack was unclear.
Doctors had to remove the tips of five of Harano's toes, because the acid had caused gangrene to develop, CNN reported.
Fukazawa, 40, denied allegations of attempted murder.