The article discusses the types of predicates, the ways of their expression, and also their functional features in the Polotsk Letters, which are a part of a set of documents known as the Polotsk Charters. It is established that there are simple verbal predicates, compound verbal predicates, and compound nominal predicates in the Polotsk Letters. All of them are expressed by typical morphological means. For example, simple verbal predicates are built up by means of the verbs having one of the 3 moods: indicative, imperative or conditional; coming in 3 basic tenses: present, past (perfect and plusquamperfect) and future (future simple, future difficult I and future difficult II); being perfective and imperfective; singular and plural; the first, the second and the third person; masculine, less often – feminine and neuter gender. The first person singular and plural verb forms, and also the second person plural verb forms are widespread because of the targeted nature of the analyzed documents. The use of singular or plural forms traditionally depended on whether the addressee of a document, the performer of the action described in the letter was individual or collective. In addition, the plural forms as verbal predicates are noted: 1) if the author of the message was a person holding a high, privileged position in the society, 2) when the etiquette formula your mercy was used, usually referring to a collective addressee. The verb forms in this syntactic function are variable as evidenced, for example, by different personal endings of verbs and participles with a final rear-lingual sound in the stem, absence or presence of a link-word in the perfect, etc., positional fixation in document composition. This is the first study of the morphological expression of types of predicates and their functioning in the Polotsk Letters. The results obtained will become the basis for a comprehensive description of the syntactic structure of both this genre variety of business texts and the entire collection of documents of the ancient Polotsk land. They will be used in writing the collective monograph “The Historical Syntax of the Belarusian Language: Parts of the Sentence”, which is being prepared at the Department of History of the Belarusian Language of the Center for the Belarusian Culture, Language and Literature Research of the NAS of Belarus.