In this study, we investigated the influence of beam hardening on the dual-energy computed tomography (DECT) values of iodine maps, virtual monoenergetic (VME) images, and virtual non-contrast (VNC) images. 320-row DECT imaging was performed by changing the x-ray tube energy for the first and second rotations. DECT values of 5 mg/ mL iodine of the multi-energy CT phantom were compared with and without a 2-mm-thick attenuation rubber layer (～700 HU) wound around the phantom. It was found that the CT density values UH, with/without the rubber layer had statistical differences in the iodine map (184 ± 0.7 versus 186 ± 1.8), VME images (125 ± 0.3 versus 110 ± 0.4), and VNC images (−58 ± 0.7 versus −76 ± 1.7) (p < 0.010 for all). This suggests that iodine mapping may be underestimated by DECT and overestimated by VME imaging because of x-ray beam hardening. The use of VNC images instead of plain CT images requires further investigation because of underestimation. [Key points] / ・The influence of x-ray beam hardening on dualenergy computed tomography (CT) was investigated. / ・CT values of iodine mapping may be underestimated because of x-ray beam hardening. / ・CT values of virtual monoenergetic imaging may be overestimated because of x-ray beam hardening. / ・Further investigation may be required for the use of virtual non-contrast images as an alternative to plain CT.