Dialogue is usually attended to as an element of fiction along with other elements, while its structural and narrative functions can also be considered. Sa’di's Bustan is among the texts which has presented these narrative functions more than other Persian texts. This paper was an attempt to investigate the relationship between the narrative functions of dialogues in Bustan and its didactic aims. The most important narrative functions of Bustan are movement, extension, and completion of story-line, consolidation of casual relationships, highlighting the oppositions, importing the embedded narratives, interpretative function and aesthetic function. The high frequency of dialogues in Bustan can be due to its didactic aims. These aims compel Sa’di to use a direct expression by narrator or characters. Because of the importance of dialogue in this didactic context, the narrative aspects of these anecdotes are the results of dialogues rather than the actions and direct description and narration of narrator. Hence, in Bustan, most of the narrative changes, conclusions, explanation of casual relationships, extension of story-line, completion of narrative sequences and etc. have been presented by dialogue rather than narrator’s narration and actors' behaviors.