The transverse dimensions of internasal and nasopremaxillary sutures in rats were assessed at different ages and following different dietary functional demands.Eighty‐four male Wistar rats were divided into two groups fed either a hard or a soft diet from 4 weeks of age, and sacrificed at 4 weeks (baseline: n = 12),16 weeks ( n = 24), 26 weeks ( n = 24), or 38 weeks ( n = 24) of age. High‐resolution micro‐computed tomograms of the internasal and left nasopremaxillary sutures were obtained with 10 µm voxel size and 5 × 5 mm field of view. The endocranial and ectocranial suture widths, the mean suture width, and the suture height were measured. Linear regression analysis was used to estimate the effects of age and type of diet on suture dimensions. Internasal and nasopremaxillary suture dimensions were influenced by age, with a generally lower width and a larger height in the older animal. Regarding diet consistency, internasal suture widths were on average larger in the hard‐diet group (e.g., mean suture width 43 µm in the hard‐ versus 30 µm in the soft‐diet group at 26 weeks). In conclusion, the internasal and nasopremaxillary sutures tend to become narrower with age, while being influenced by masticatory functional demands.