mulla sadra (979-1050 AH) and Parmenides (510-340 BC) are two of the most distinguished figures in the field of philosophy who have influenced philosophical thought with their innovations concerning the most important philosophical issues.Although one belongs to the era of the beginning of philosophical thought in ancient Greece and the other rose in a period in which his different thought was in its culmination, their theories of "being" are sometimes very close to and sometimes far from each other.Here, the writer first deals with the approaches, worldviews, and methods of the two philosophers regarding "being". Then she reveals what the meaning of this issue for each of them is and describes how they sometimes come close to and sometimes go far from each other in this regard. Firstly, both of them agree that "being" is real, base phenomena on "being", and maintain that anything other than it is unoriginal. Secondly, both believe that it is possible to demonstrate the principiality of "being" by means of logical reasoning. Thirdly, although their analyses are different, knowledge enjoys an ontological basis in their philosophies. For them, there is an agreement between thought and being; thought perceives being, which is not an abstract and mental issue. Nevertheless, mulla sadra and Parmenides move away from each other when they explain the kind of "being" and the mode of its principiality and actualization. This is because each of them follows a specific purpose.