The participating teams are made up of local Thai celebrities, professional horse polo players, and even former rugby players from New Zealand's All Blacks team.
Robin Brooke, a former New Zealand rugby player, has been competing at the tournament for 6 years.
"It's a very, very challenging event, playing polo on elephant is quite unusual, when you tell people what you're doing, 'I say I'm going to Thailand to play elephant polo', and the first question back is 'You mean on elephants?' And I say, 'yes, of course'. But we play against the teams are seeded, we play against all sorts of other teams from all over the world. But mainly the good players on the other teams are from countries that produce excellent horse polo players, Germany, India, we haven't had any Argentineans, but they are extremely good even on elephants."
Tim Boda, the tournament organizer, said the elephants who get selected to play in the competition are well cared for.
"The 21 elephants we are playing with here are from Surin, some of them have a great life where they come from, some not. We have built a little sanctuary for them here, we have our vets (veterinarians) here that will do checkups. They get their vitamins, they're well fed, and compared to the unfortunate working hours they sometimes have to put up with, here it's ten minutes for each elephant, the rest of the day they are almost having a holiday here with us and we really take care of them well."
During the tournament, the elephants consume high energy food daily including 20 stems of bananas, 50 sticks of sugarcane and 10 pineapple plants.
Most of the elephants are those who normally walk the streets with their mahouts, or minders, or elephants working long hours in trekking camps.
Only the young elephants that like to run around can join the polo sessions, with each of them limited to 10 minutes on the pitch daily.
Spectator Nicola Winter says it's a great day out.
"I really think it's an amazing event, especially now for me the first time in Bangkok, with the Chao Phraya in the back, and I think it's just amazing with the big tent and lots of food and nice people, and I think the elephants are still a bit nervous, but they are getting more calm every game."
The organizers of this year's event are hoping to raise about 15 million baht, or over 410 thousand U.S. dollars, for various elephant welfare projects.
The projects may include protecting wild elephant territory, policing and ranger training to protect the elephants in the wild, and also mitigating human-elephant conflict.
The annual event has so far raised over 1 million U.S. dollars for elephant causes since it started in 2001.
For CRI, I'm Xie Cheng.
