The award, for an unprotected fleece, attracted entries from New Zealand, Australia, Argentina and South Africa.
The Dempsters provided two of New Zealand's three entries.
The last three times the Dempsters had entered the competition, which was run under a different format this year, they had won it twice and come second once.
Mr Dempster said he entered six fleeces in this year's contest, but was not certain which won the award.
He thought it might have been a 15.2 micron fleece off a four-tooth wether.
If it was, it weighed 3kg and yielded 77%.
Mr and Mrs Dempster farm the 4000ha property The Hummock, 26km inland from Waikouaiti, and have farmed merinos since 1990-91.
They, along with Mrs Dempster's father Tony O'Malley, bought merinos during the resurgence in interest in the late 1980s-early 1990s, and they have maintained their flock, which today numbers 2200 ewes, 1700 hoggets and 500 wethers.
They also run 2300 crossbred ewes and 600 hoggets.
He said East Otago was excellent wool-growing country, producing fibre that was clean, brightly coloured and high yielding.
They buy rams from John and Susan Elliot's Lammermore Stud, at Paerau, which is based on the Rockbank flock in Victoria, Australia.
Mr Dempster said the merinos were kept on tussock country.
Whenever the sheep were in the yards, he looked for any that had exceptional fleeces and these were then kept separate.
From there, Andrew McNeill, of Wool Partners International, and Mr Dempster's wool classer, Graeme Bell, helped prepare the entry.
For their efforts they won a trophy, merino fabric to make a suit and limited edition art work.
