The present paper aims to examine one of the nominalization phenomena of Koryak (the Chukchi-Kamchatkan language family)—agent nominals and patient nominals derived from intransitive or transitive verbs through suffixation of -j-olqəl(JQ hereafter). In particular, this paper aims to ascertain the followings: (a) There is a hierarchy of the degree of JQ nominalization according to grammatical functions in sentences. That is, the degree of nominalization decreases in the following order: nominal argument > noun modifying phrase/clause > predicate of the main clause. (b) Even the nominal argument in the highest hierarchy exhibits limited case marking and thus does not obtain the same morphological and syntactic properties as a prototypical noun. (c) Predicative JQ in the lowest hierarchy of the degree of nominalization obtains certain verbal meaning and syntax in the following phenomena: i) Similar to a finite verb, it takes a nominal argument, that is, transitive subject, in the absolutive case. ii) Similar to a finite verb, it takes oblique cases and adverbs. iii) It obtains a modal meaning of obligation. Through the analysis of JQ, this paper also reveals that predicative JQ exhibits both syntactic and semantic similarity to the “noun-concluding sentence” found in a number of languages, including Japanese. This suggests that a cross-linguistic study of noun-concluding sentences is possible not only from those data of languages with syntactic noun-concluding sentences but also from that of some other languages with morphological noun-concluding sentences.