Summary: This paper models and formalizes a mobile logic programming multi-agent system for mobile environments. Such a system consists of a number of agents connected via wire or wireless communication channels. Agents communicate with each other via passing answer sets obtained by updating the information received from connected agents with their own private information. The interactions between agents are also modeled in this formalization. Based on this model, knowledge based transaction can be studied in such a mobile multi-agent system. In addition, knowledge transaction is formally defined and modeled for these mobile multi-agent systems.