Abstract: As transactions in distributed real time database systems have to meet the timing requirements, such as deadlines, in addition to the well known characteristics of ACID for transactions in conventional database systems, the traditional transaction commitment protocols and real time commitment protocols developed could not guarantee the atomicity of real time transaction. In this paper, atomic commitment of distributed real time transactions and its correctness criteria, taking deadlines into account, are described first. Then a real time atomic commitment protocol-RTACP for distributed firm and soft deadline transactions is presented, which could ensure the atomicity of distributed real time transactions and improve the performance of distributed real time database systems.