Jimenez made 32 appearances across all competitions for Bournemouth last season, but the Spaniard was dropped in May as the Premier League club omitted him from their squad while investigating social media posts linked to the player.
Bournemouth did not provide further details and Jimenez did not respond to requests for comment made to his representatives at the time.
Fiorentina did not disclose the financial terms of the deal, although Italian and British media reported the option to buy is worth about 20 million euros ($22.88 million).
"ACF Fiorentina announces that it has acquired, on a loan basis with an option to buy, the sporting rights of player Alejandro Jimenez Sanchez from AFC Bournemouth," the Italian club said in a statement.
Jimenez joined Bournemouth permanently from AC Milan in February after an initial loan spell and made 31 Premier League appearances last season, scoring one goal.
A product of Real Madrid's academy, Jimenez moved to Milan in 2023 before joining Bournemouth, where he established himself as a regular in the first team.