Tanaosri Trail 2026 - Ratchaburi, Thailand

The Tanaosri Trail 2026, themed Deep Roots, Hard Routes, returns to the Natural Science Park in Suan Phueng, Ratchaburi, for a demanding weekend of mountain and forest running near the Thai-Myanmar border. Organiser information schedules activities across 18-20 December, with the five competitive or participation starts on Saturday 19 and Sunday 20 December (Thailand time, UTC+7).

Mountain courses and cut-offs

• Tanaosri Trail 100: 104 km, approximately 5,510 m of ascent, starting 09:00 Saturday 19 December; 29-hour limit, closing at 14:00 on Sunday.
• Tanaosri The Legend 50: 51 km, 2,740 m of ascent; 06:00 Saturday, 14-hour limit.
• Tanaosri Little Boy 25: 26 km, 1,590 m of ascent; 04:00 Sunday 20 December, 10-hour limit.
• Tanaosri Fun Trail 10: 11 km, 430 m of ascent; 07:00 Sunday, 5-hour limit.
• Tanaosri Family Run 4: 4 km, 100 m of ascent; 15:00 Saturday, 2-hour limit.

The race names use rounded labels (100K, 50K, 25K and 10K), whereas the organiser specifies actual course distances of 104, 51, 26 and 11 kilometres respectively. Trail terrain and climbing make pace and fitness planning particularly important. The 100K route carries an ITRA 5 classification in the organiser's race specifications, while the 50K and 25K are advertised as ITRA 3 and 1 respectively.

Experience requirements and safety

The organiser requires prior successful completion of a 50K or longer trail for the 100K; a marathon, five half marathons or a trail of at least 30K for the 50K; and a marathon, three half marathons or a trail of at least 20K for the 25K. The 11K requires prior mini-marathon experience; the 4K Family Run has no comparable minimum. Runners should read the published compulsory equipment rules for their category, prepare for remote mountainous terrain and carry appropriate hydration and navigation equipment.

Registration and race-week information

The current-edition registration provider displays all five distances as open, subject to places being available at checkout. It lists current category prices higher than some early-bird figures still shown on the organiser's website. Use the live registration link for the actual amount. The organiser-linked 2026 booking form offers collection appointments on Friday 18 December, 13:00-19:00, and Saturday 19 December, 08:00-18:00 at the race precinct; not every slot necessarily suits every category. The same form contains a stale 2025 collection option, which should not be used for 2026 planning. Confirm your applicable collection appointment and required original identification with the organiser.

The official programme and route descriptions are on the Tanaosri Trail website. Check the final participant guide for checkpoint rules, compulsory kit, route changes, medical support, and weather-related operational notices before travel.