This article presents a description and analysis of the deontic modality and its relationship with mood category (realis vs irrealis) in Paresi, a language of the Arawak family, spoken in Brazil. Data were collected from two questionnaires on deontics and texts. For the analysis of the data, we used, as the theoretical framework on mood and modality, the works of Feldman (1986), Hacquard (2006, 2010); Mithun (1995, 1999) and Palmer (2001). First, we show how the realis/irrealis mood marking occurs in Paresi. In the sequence, we describe the Paresi as a language that lexically marks the type of modality, but not the modal force. We present two markers of deontic modality in this language: maika and wa(iye)hena, which indicate both necessity and possibility. These markers exhibit particle properties and occupy high positions in the sentence structure. Finally, we describe the deontic modality of necessity, showing that there are two types of obligations in Paresi: one indicated by the maika particle; and another, by the particle wa(iye)hena. The first figures, preferably, in contexts in which a participant is directly responsible for the realization of the event and seems to be associated to the realis mood. On the other hand, wa(iye)hena is employed in contexts of laws and general rules, which describe how a state of affairs should be, and co-occurs, predominantly, with the irrealis marker.