Speech disfluency in children can be increased or decreased depending on the type of linguistic task presented to them. In this study, the effect of sentence imitation and sentence modeling on severity of speech disfluencies in preschool children with stuttering is investigated. In this cross-sectional descriptive analytical study, 58 children with stuttering (29 with mild stuttering and 29 with moderate stuttering) and 58 typical children aged between 4 and 6 years old participated. The severity of speech disfluencies was assessed by SSI-3 and TOCS before and after offering each task. In boys with mild stuttering, The mean stuttering severity scores in two tasks of sentence imitation and sentence modeling were 21.81 ± 1.72 and 12.94 ± 1.38 respectively (P = 0.837). But, in boys with moderate stuttering the stuttering severity in the both tasks were 23.79 ± 1.26 and 29.00 ± 2.03 respectively (P = 0.004). In girls with mild stuttering, the stuttering severity in two tasks of sentence imitation and sentence modeling were 13.14 ± 2.47 and 13.86 ± 2.03 respectively (P = 0.094). But, in girls with moderate stuttering the mean stuttering severity in the both tasks were 25.27 ± 1.93 and 33.18 ± 2.32 respectively (P = 0.007). In both gender of typical children, the score of speech disfluencies had no significant difference between two tasks (P > 0.05). In preschool children with mild stuttering and peer non-stutters, performing the tasks of sentence imitation and sentence modeling could not increase the severity of stuttering. But, in preschool children with moderate stuttering, doing the task of sentence modeling increased the stuttering severity score.