Sandra Jacqueline McMahon, 68, has been jailed for six years and nine months for cannabis dealing.

Wellington's grass dealing granny has gone to prison for six years and nine months.

Sandra Jacqueline McMahon, 68, and another family member ran a cannabis selling operation out of a Newtown flat, making profits the police estimate were up to $7.9 million in the past seven years.

Police following her in June saw her make deliveries and pick up pounds of cannabis, often in the carparks of supermarkets. Justice Alan MacKenzie at the High Court in Wellington today said there were up to 22 sales a day noted by police.

A search of a flat and another premises found cash, cooler bags full of cannabis and packaging equipment ready to go.

Bank account records showed multiple deposits, using a fast deposit envelope system to avoid bank tellers.

McMahon and her family member were on benefits at the time or unemployed and she was on superannuation.

They had up to 150 regular customers purchasing weekly.

Family also had money deposited into their bank accounts and their properties renovated.

Justice MacKenzie said it was one of the most serious cases of its type.

"You acknowledge your personal involvement for 10 years and that the motivation was profit. Even when you became aware of police surveillance you continued." he said.

McMahon had seven previous convictions from between 1992 and 1995 for selling or supplying cannabis.

She had admitted to police that the current operation had been going for up to 10 years, but maintained she and her co-offender, who is awaiting trial, maintained separate client lists despite using the same suppliers and properties.

The judge said she was remorseful for her family but McMahon's remorse for the offending was minimal.

McMahon had pleaded guilty to five charges of possessing cannabis for supply, one of money laundering and one of selling cannabis.