The 22-item lot, the first items of which opened for bids on Saturday, includes shirts from high street chains Reiss, Filippa K, and Banana Republic, as well designer clobber from the likes of DKNY, Marni, Chloé and YSL.
Alongside the high street fashion are some more rarified items: A coat by Italian designer Alberto Biani, a shirt from Ultra Ozbek, and some high heels from France's Roger Vivier.
The priciest item on the auction at present was a pair of Dolce & Gabbana knee-length boots -- which sold on Tuesday for more than 2700 kroner ($440).
"Many of our clothes can be reused rather than discarded," the 40-year-old wrote introducing the sale on the auction side Bloppis.no. "Protect the environment in a fun and easy way."
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The auction, which opens on November 30th, Mette-Marit's second on Bloppis. She sold off another batch of clothes in June last year. All proceeds will go to Miljoagentene, an environmental charity.
Mette-Marit is currently recovering from surgery on the slipped disc which has stopped her fulfilling her official duties since the start of October.