The company's Japanese unit, referencing the animated film "Alice in Wonderland", took to social media on Sunday with a message about the movie's well-known "unbirthdays".
The original English tweet wished followers a "very merry unbirthday".
In Disney's original film, characters celebrate an "unbirthday" -- every day of the year except their own birthday -- during a party with Alice.
However, the Japanese tweet's wording translated as "a day of nothing" -- and coincided with commemorations for the more than 74,000 people killed when the US dropped an atomic bomb on Nagasaki.
Disney quickly deleted the tweet on Sunday, following a string of online criticism.
"We deeply apologise for using an inappropriate expression that could annoy people," it tweeted on Sunday.