This study evaluates seismic vulnerability of low-rise RC frames in northern Thailand using damage observations from the 2025 Mandalay earthquake. Field surveys documented 137 buildings (1-6 stories) in Chiang Mai, with damage primarily to infill walls. Analytical fragility curves were developed using nonlinear time history analysis of 7 representative buildings and calibrated with observed damage. Results indicate high vulnerability with over 50% probability of significant damage under design-basis earthquakes. Authors: Arnon Sunatai, Jarun Srechai, Wongsa Wararuksajja, Sutat Leelataviwat. Presented at TSER2025 Symposium, Bangkok, August 2025.