This randomized controlled clinical trial evaluated the color change of teeth bleached with either hydrogen peroxide (HP) or ozone (OZ). A total of 26 patients with a mean age of 36.2 years (SD, 8.7 years) who met the inclusion criteria were enrolled in the study. The subjects were randomly assigned to receive chairside bleaching using 40% HP or gaseous OZ. Maxillary dental arch vacuum trays were constructed with circumferential openings in the middle portion of the maxillary incisors at their labial surfaces. These trays were used for measuring color-first at baseline and then immediately and 48 hours after postbleaching-and were not used in bleaching. Changes in color were determined using CIE L*a*b* coordinates. Analysis of the data revealed that, while overall color change (ΔE*) values of the HP and OZ groups did not show statistically significant differences immediately after bleaching (P = 0.114), ΔE* values were significantly different 48 hours postbleaching (P = 0.00). Visible color changes were not obtained with either HP or OZ immediately postbleaching. The greatest visible color change occurred with HP 48 hours postbleaching.