South Australian Liberal Senator Mary Jo Fisher has been charged over an incident at an Adelaide supermarket.

Senator Fisher is accused of attempting to leave the supermarket at Frewville, in Adelaide's east, without paying for some goods on December 15 last year.

It is also alleged she assaulted a security guard who tried to stop her from leaving.

In a statement, Senator Fisher confirmed she had been charged over two matters, but will vigorously defend them.

She says there will be a hearing in September where she will present her defence, but did not give any details on the charges.

One of the Senator's close friends says she has been struggling with serious depression and that her parliamentary colleagues have been concerned about her struggle.

Senator Fisher is originally from Western Australia, and was elected to the Senate in 2007.