Riders in last year's Mongol Derby.
Competitors must complete the race within 10 days, changing their native horses at specially set-up stations at intervals of no more than 40km.
Its promoters say the derby celebrates the horseback messenger system used by the warrior Genghis Khan.
The derby is organised by a British company, The Adventurists, in collaboration with the Mongolia-based Tengri Group.
The race, billed as an event of rider endurance, involves about 1000 horses.
Each station, known as an urtuu, will consist of a small collection of gers - canvas and felt tents - and the horses will be stationed at each point ready for the following leg.
Each urtuu will be hosted by a Mongolian nomadic herding family and manned by a locally trained veterinarian.
The organisers say they have worked with some of Mongolia's top horse breeders and a network of Horse Racing Associations to gather horses for the race.
All will be vet-checked before participation and assessed following competition.
Some concerns were voiced before last year's inaugural running of the event, focused mostly on horse welfare worries. However, a report furnished by Jenny Weston, an International Equestrian Federation-accredited four-star endurance vet, indicated only minor problems.
"I was impressed with the tough nature of the local horses (rude to call them a pony even though they only ranged in height from 12 to 14.2 hands)," she wrote.
"I spent more time providing veterinary services to the locals for their livestock and first aid for humans (riders and locals) than attending to the horses that were participating in the derby."
The 2009 running involved 26 riders. South African architect Charles van Wyk, 28, was declared joint winner with Mongolian rider Shiravsambo Galbadrakh.
Weston returns as chief vet for this year's event and, with colleagues at New Zealand's Massey University, developed and delivered a curriculum to ensure the horses were properly conditioned before the race. They have also worked to help the Mongolian vets raise standards of veterinary care across the country.
Early in June, in association with the university, 20 Mongolian equine vets were trained by Weston for their role in the event.
The nine-day course was split between classroom training in Ulaanbaator and practical vetting.
The intention is that the training programme will take place each year to provide a lasting veterinary legacy in Mongolia.