A man has been caught trying to smuggle about 7000 illegal steroid tablets into Australia in his underwear.

Customs officers at Melbourne Airport stopped the man, who arrived on a flight from Bangkok, when they suspected he was concealing something inside his clothing on Friday.

A search revealed about 7000 tablets, believed to be Dianabol, concealed in four snap-lock plastic bags inside his underwear.

Officers also found a 100ml bottle labelled "Finexol" and 100 "Trenabolone Acetate" tablets.

A 23-year-old New Zealand man has been charged with smuggling prohibited imports and is due to face the Melbourne Magistrates' Court on September 17.

The maximum penalty for the offence is five years jail and/or a $110,000 fine.

AAP