Few studies have investigated the interaction of ultraviolet (UV)-B radiation and CO2 concentration on plants. We studied the combined effects of UV-B radiation and CO2 concentration on canola (Brassica napus cv. 46A65) under four growth conditions – ambient CO2 with UV-B (control), elevated CO2 with UV-B, ambient CO2 without UV-B, and elevated CO2 without UV-B – to determine whether the adverse effects of UV-B are mitigated by elevated CO2. Elevated CO2 significantly increased plant height and seed yield, whereas UV-B decreased them. Elevated CO2 ameliorated the adverse effects of UV-B in plant height. UV-B did not affect the physical characteristics of leaf but CO2 did. Certain flower and fruit characteristics were affected negatively by UV-B and positively by CO2. UV-B did not affect net photosynthesis, transpiration and stomatal conductance but decreased water use efficiency (WUE). Elevated CO2 significantly increased net photosynthesis and WUE. Neither UV-B nor CO2 affected chlorophyll (Chl) fluorescence. UV-B significantly decreased Chl b and increased the ratio of Chl a/b. Elevated CO2 decreased only the ratio of Chl a/b. UV-B significantly increased UV-absorbing compounds while CO2 had no effect on them. Both UV-B and CO2 significantly increased epicuticular wax content. Many significant relationships were found between morphological, physiological, and chemical parameters. This study showed that elevated CO2 can partially ameliorate some of the adverse effects of UV-B radiation in B. napus.