In this paper, we would like to obtain the effect of the quantum backreaction on inflationary Starobinsky cosmology in spatially flat D-dimensional Friedmann–Robertson– Walker universe. For this purpose, first, we obtain the vacuum expectation value of energy–momentum tensor, which is separated into two parts, UV and IR. To calculate the UV contribution, we use the WKB approximation of the mode function of the equation of motion. Since the obtained value of this contribution of the vacuum expectation value of energy–momentum tensor is divergent, we should renormalize it. Therefore, by using the dimensional regularization and introducing a counterterm action, we eliminate divergences. After that, we calculate the contributions of IR part and trace anomaly. Thus, we obtain the quantum energy density and pressure during inflation era in this model. Finally, we can find the effect of backreaction on scale factor in inflation era, which leads to the new scale factor.
