Abstract To better constrain the post‐collisional southward displacement of the Indochina Block (ICB) and the crustal deformation of the southeastern Tibetan Plateau, we present a reliable paleomagnetic study of Upper Cretaceous Nanxin Formation redbeds exposed in the Lanping area, at the northern edge of the Lanping‐Simao Terrane (LST). The tilt‐corrected site‐mean direction derived from 30 sites is Ds = 39.3°, Is = 48.4° with α95 = 4.3°, corresponding to a paleomagnetic pole at 55.3°N, 175.5°E with dp/dm = 3.7°/5.6° and a paleolatitude of 29.4°N ± 3.7°N for the sampling area (26.6°N, 99.4°E). This paleomagnetic data set passes both positive fold and reversal tests at 95% and 99% confidence levels. Comparison with the Late Cretaceous pole of the South China Block and the East Asia apparent polar wander path shows that the entire ICB underwent a coherent southward displacement of ∼900 km between the Late Cretaceous and Late Eocene.