This study represents the first attempt to elucidate and detail the types of misconceptions high school students hold relating to basic concepts and topics of nuclear chemistry. A diagnostic multiple-choice test was administered to 157 tenth-grade students (15-16 years old) and the data were analyzed. The results show that high school students hold a series of misconceptions both about nuclear chemistry topics related to nuclear stability, half-life, binding energy, practical applications of nuclear chemistry, radioactive decay rate, and about basic chemistry concepts that are essential prerequisites for learning nuclear chemistry. One of the obstacles to effective learning in nuclear chemistry is that concepts and topics related to it are quite abstract. The fact that students fail to link between macroscopic and microscopic levels of representing matter causes them to use the concepts atom, element, and matter interchangeably. Furthermore, these results identify that the students have neither comprehended the concept of isotope atom nor understood exactly the fact that elements can contain different naturally occurring isotopes. In addition, students demonstrated confusion about the difference between nuclear and chemical reactions. We offer some suggestions for a more effective teaching approach to ensure better learning of nuclear chemistry. One of the implications for teaching is that initially high school chemistry teachers should ensure that students have pre-existing knowledge before starting to teach them the topics related to nuclear chemistry. Teachers also need to emphasize the distinction between chemical and nuclear reactions by using examples. They should provide students with awareness of both the useful applications of nuclear chemistry in daily life and the harmful effects of radioactivity, which are always on the agenda but not given sufficient attention as they are usually placed in the last chapters of chemistry textbooks. (Contains 1 table and 2 textboxes.