It is known that axial compressive deformation is usually generated in a stone column under vertical loads, and often accompanied by a radial expansion against the surrounding soil near the top portion of the column. With the consideration of this deformation characteristic of the stone column, a new technique to measure the lateral bulging of the stone column was proposed, where the lateral bulging of the column was determined by circumferential measurements. The variability and accuracy of the proposed measuring technique was fully verified by the comparison with the other measuring methods. Moreover, this measuring technique was employed to study the deformation behavior of stone columns in an indoor laboratory test. The measuring results show that the lateral bulging of the stone column increases with the increase of vertical loads. Furthermore, under a certain load, the column bulging increases along with the column length firstly, then decreases with the column length after the maximum bulging.