The accounts for last year showed a profit of $2 million.
The accounts of last year showed a profit of $2 million.
Which one is correct? My idea is that both of them is OK, anybody can confirm it?
"Accounts for last year" seems more common in financial reports I've read, and also, as Sean Duggan says, avoids possible misunderstanding of the meaning.
Usually the context would be sufficient to avoid any ambiguity, so either is probably alright. According to google ngrams, the two phrases occur with similar frequency. However, 'last year's accounts' is far more common than either.