Today, some tens of million years after its creation by the collision between India and Asia, the Tibetan Plateau is the highest and largest plateau on Earth. Results of geological and tectonic studies indicate that the plateau is extending. However, almost no quantitative evidence shows whether the plateau is still uplifting or thickening nowadays. Herein, we present geodetic evidence of mass loss beneath the Tibetan Plateau and increasing crust thickness. Combined absolute gravity and Global Positional System (GPS) measurements at three stations in southern and southeastern Tibet during two decades reveal uplifting of the Tibetan Plateau at a millimeter-per-year level, but its underlying mass is diminishing, indicating that the crustal thickness is increasing at an annual millimeter to decimeter level.