Mrs Mason said rotary club members would be marking out stall spaces on Thursday.
She said the club was hoping for fine weather after a "weather bomb" last March forced organisers to postpone the fair for the first time.
"We're watching the long-term forecast and hoping for the best," Mrs Mason said.
The fair will feature about 500 stalls, from clothing and food to furniture and kitchenware.
New food on offer will include cinnamon and apple donuts and Stewart Island salmon.
Mrs Mason said the club was expecting a 30,000 attendance as the March fair is generally bigger than February's.
"The weather's a bit cooler and by now families have paid school fees, the Christmas budget is out of the way and people have got a bit more money to spend," she said.
The fair will also feature sideshow attractions, including a bungy jump machine, water wheel pools and Segway machines.
The club hopes to raise about $75,000 which goes into the Martinborough Fair Trust and is redistributed to charities and organisations during the year.
"All the money raised goes to charity.
"[It's a] huge fundraising opportunity for the district and most of it stays in Wairarapa, we do have some international projects that we support," Mrs Mason said.
She said local businesses would also benefit from the fair.
"It's just a fun day out for everybody and it brings a lot of people to Martinborough.
"Most of the shops open that day and they generally find their turnover is much bigger than on a normal weekend."
The fair starts at 8am in The Square.
