The basic concept of sociology has been regarded as "action". This kind of thought, has long theoretical accumulations after Max Weber and holds a central position in social theory. Against this tradition, however, Niklas Luhmann suggests that the concept of meaning should be basic. According to him, meaning is more suitable to describe the contingent possibility of the "world". And he introduces phenomenological insights into his framework of system theory, building it up into the theory of autopoietic systems of communications. In this paper, the author tries to summerize his discussions on meaning and communication in the first place, and examines his most important conception like self-reference (Selbstreferenz) and self-observation (Selbstbeobachtung) in the next. In conclusion, the author (1) critisizes the ambiguity of his concept "self-reference" and (2) points out theoretically fruitful possibilities of observing self-observational systems which always deparadoxize its own paradoxes.