The article considers poetic, thematic and compositional features of the early English chivalric romance “Sir Isumbras”. This is a pilot study for Russian literary criticism, and its relevance is due to the insufficient research into this medieval poem in English-language literary criticism. The objectives of the study are to describe the strophic organization of the text variants of the romance found in different manuscripts, its correlation with the strophic organization of the poetic hagiography sample “The Life of Saint Eustache”, presented together with “Sir Isumbras” in MS Ashmole 61, and to consider plot motifs common to this novel and the works of various genres including the indicated hagiography and the chivalric romance “Sir Gowther”, as well as the composition specifics of plot scenes, the features of narrative techniques and the placement of plot accents. In the process of analysis, we have established that the main unit of strophic organization is the twelve-line tail-rhyme stanza of chivalric romances, however, the six-line stanza, usual for lives of the saints in verse, also has a large share; the plot of the novel is connected with different genres and subgenres and includes their characteristic motifs; the composition of the plot scenes is distinguished by two types of symmetry - both mirror and stepped; the forms of psychologism are still absent, but there are heroes’ stereotyped actions characteristic of folklore and associated with their emotional state whose verbal expression is similar to oral poetry formulas; finally, the emphasis of the final battle scene determines the meaning of the novel and gives it the features of a certain subgenre.