A Catholic school student has been accused of dealing drugs at their Year 12 formal.

Police were called to the St Kevin's College Year 12 formal at Melbourne Park on Tuesday night.

A parent is said to have noticed suspicious behaviour in the toilet cubicles and called police, The Age was told.

Police attended just before 9pm, a Victoria Police spokeswoman said, and spoke to an 18-year-old.

They seized his mobile phone, an amount of cash and a number of capsules believed to be MDMA.

"The man was not fit for interview on the night and is expected to be interviewed at a later date," the spokeswoman said.