A built-up environment utilizes building materials containing natural radionuclides that will change radiological risks. While radiological risks have been estimated from the activity concentrations of natural radionuclides in soil, it is important to evaluate the changes of these risks for the built-up environment using these building materials. Based on the direct measurements of absorbed dose rate in air and calculation of absorbed dose rate in air from activity concentrations in soil for all of Vietnam which has undergone significant economic growth in recent decades, the changes of absorbed dose rate in air and radiological risks before and after construction of many artificial structures were investigated. The results showed that the absorbed dose rates in air were clearly changed by the urbanization, and the difference ratio for all of Vietnam ranged from 0.5 to 2.1, meaning that the artificial structures have been acting as shielding materials to terrestrial gamma-rays or radiation sources. However, changes in annual effective dose in the built-up environment were small, and there was no new radiation risk from the built-up environment for Vietnam.