A Sydney mother accused of trying to smuggle 1.5kg of crystal methamphetamine through a Malaysian airport is expected to be charged today.

The 51-year-old woman, believed to be a mother of four, was travelling from Shanghai to Melbourne via Kuala Lumpur when she was intercepted by authorities.

Customs officials allege they discovered the drugs in her baggage. She is expected to appear in court tomorrow.

She was arrested and remains in police custody.

The Department of Foreign Affairs is assisting the woman, and if she is found guilty of trying to smuggle drugs, she faces a mandatory death sentence.

Mandatory death penalty applies for anyone caught with at least 50 grams of of the drug 'ice'.

TODAY Show legal expert Sam Macedone said Malaysia's drug laws were "harsh and serious".

"If you get convicted of drug trafficking over in Malaysia you face the death penalty," he said.

"And the death penalty is usually by hanging.

"If she is convicted, there is only one sentence and it's the death sentence."

Malaysian customs chief Chik Omar Chik Lim said the woman was arrested on December 7.

Anyone with at least 50 grams of the drug is considered a trafficker in Muslim-majority Malaysia, which imposes a mandatory sentence of death by hanging upon conviction.

The woman is expected to appear in court today as authorities seek to extend the initial seven-day period of remand for criminal suspects.