To study the effect of growth rate on fibre characteristics and their variations in Norway spruce, trees were sampled in a nutrient optimisation experiment in northern Sweden. Data was collected from 24 trees (40 years old) from fertilised and control plots after 12 years of annual nutrient application, as well as from older trees outside the experimental area. Fibre length, fibre diameter, cell wall thickness, lumen diameter and cell wall percentage were measured from every third annual ring at breast height and at a height of 4 m. Fibre properties, as well as their standard deviation, were closely related to ring number and distance from the pith. Intra-ring variation of fibre characteristics was high compared to their variation between trees. Fertilisation reduced fibre length and cell wall thickness, but increased fibre and lumen diameter in rings of the same age. The difference in fibre width, cell wall thickness and lumen diameter between fertilised and control trees was less apparent, but a greater difference in fibre length was found between the treatments with regard to distance from the pith. There was a similar effect of fertilisation on fibre properties in early- and latewood. The effect of enhanced growth rate was less pronounced at a height of 4 m (near the pith) than at breast height (in older rings). It was demonstrated that it is possible to model intra-tree variability of fibre characteristics using ring width and cambial age as independent variables. Models presented are, however, limited by the relatively young age of the sample trees used.