Dasilva, 19, is yet to play for Chelsea but impressed in 10 appearances for the Addicks at the end of last season.
The full-back captained England Under-19s to their first win at the European Championship this summer, as the Young Lions beat Portugal 2-1 in the final.
"He brings pace, talent, desire and a willingness to improve," Charlton boss Karl Robinson told the club website.
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Jay Dasilva has signed a new four-year deal with Chelsea and rejoined Charlton Athletic on a season-long loan.