The objective of this study was to assess loblolly pine fiber properties within-tree variation. We determined fiber properties using fiber analyzer in conjunction with near-infrared spectroscopy (NIRS). Diffuse reflectance NIR spectra were collected from samples, age 19-31 acquired from across the Southeast in 10-mm radial sections from pith to bark. A subset of the samples were selected based on their NIR spectra uniqueness, macerated, and the fiber properties determined. Calibration models developed for fiber length were strong (R2=0.88, SECV=265-m, RPD=2.9). However calibrations for fiber width were moderate (R2=0.48, SECV=1.99-m, RPD=1.40). The calibrations were checked with a prediction set, and their performance was again strong for fiber length (R2=0.84, SEP=0.261-mm, RPD=2.50) and moderate for fiber width (R2=0.49, SEP=0.0018-mm, RPD=1.39). Within-tree variation of fiber length shows that it is low at the base of the stem and increases with height in the butt log. Fiber length increases from pith to bark, and the rate of change occurs at a faster pace at higher heights than near the stem base. Fiber width follows a similar trend to fiber length.