An automatic phantom scanning system was developed at our laboratory. Its performance

i.e. the percentage depth-dose curves and off-axis ratio curves

was tested on an Elekta Precise linac with 6 and 18 MeV electrons

and their X-rays. The results were compared with the Blue Phantom system

the most advanced water phantom system in the world. The curves obtained from the two automatic water phantom systems agree perfectly. The error of the percentage-dose in the corresponding depth for photon beams is less than 1%. The error of the percentage-dose in the corresponding depth below maximum dose point for electron beams is less than 1%

too. Off-axis ratios of fields for photon and electron beams are consistent. This indicates that its performance is as good as the advanced phantom.