This descriptive-analytic study aimed at investigating the semantic interaction of negation with the epistemic and deontic possibility and necessity senses of a select group of central Persian modal verbs (i.e., tavanestan, shodan, momken budan, emkan dashtan, bayestan and lazem budan). Among these modal verbs, the first four express the notion of possibility and the rest express necessity. Necessity and possibility constitute the core of modality domain. Modality as a semantic category mainly deals with speaker’s attitude or opinion regarding the state of affairs. Epistemic and deontic modality are the two main types of modality. The former expresses speaker’s judgment regarding the truth or falsehood of propositions while the latter deals with speaker’s influence on actualization or non-actualization of actions. Modal verbs are among the commonly used modal forms in Persian. Negation has logical and semantic interactions with modality (especially, possibility and necessity notions). Negation appears in Persian modal verbs and main verbs as ن- prefix. In this study, the views of Palmer (1995) and de Haan (1997), who both investigated the interaction of negation and modality from typological point of view, were used as the theoretical framework. The examples used as evidence in our analyses were mainly extracted from the corpus of Academy of Persian language and literature. The study showed that the interaction of negation prefix with the modal verbs of possibility domain (i.e., tavanestan, shodan, momken budan and emkan dashtan) is “regular” in the sense that there is correspondence between the form and meaning of the negative modal verbs. Thus, a negative modal form negates the modality and a negative main verb negates the proposition. In the necessity domain, the interaction of lazem budan with negation prefix is, also, “regular”. In fact, the co-occurrence of negation prefix with bayestan negates the proposition (not the modality). In addition, bayestan cannot express the epistemic “lack of necessity” of the truth of a proposition and deontic lack of necessity for actualization of an action. Other modal verbs (e.g., lazem budan and modal verbs of the possibility domain) express these notions through “modal suppletion” or “logical suppletion” strategies. Bayestan is a “uniscopal” modal form interacting only with “narrow scope” negation while other modal verbs investigated in this study are “biscopal” as they interact with both narrow and wide scope negation. Except bayestan, for which “modal suppletion” and “logical suppletion” strategies are employed to express wide scope negation, for other verbs investigated in this research “negation placement” strategy is used to distinguish between narrow and wide scope negation.