Background: Tissue dielectric constant (TDC) and spot bioimpedance measurement (BIA) have a role in the assessment of tissue composition changes in breast cancer-related lymphedema (BCRL). Our aims were to determine whether TDC and spot BIA measures could detect inter-limb differences in BCRL, explore the relationship between methods, and establish the intra-rater reliability and technical error of measurement for TDC. Methods and Results: Women with (n=20) and without (n=4) unilateral BCRL participated. Circumference, TDC, and spot BIA measures were completed on the most affected region of the arm for BCRL participants and at a standardized forearm point in women without lymphedema. All measures were compared to measurements from an identical location on the contralateral arm. The affected arm differed significantly to the unaffected arm of women with BCRL for TDC and spot BIA measures. The median (IQR) differences were: extra-small probe 5.75 (3.10-8.21), small probe 3.50 (1.16-6.89), medium probe 5.08 (0.88-10.91), and for spot BIA measurement (-35.20 Ω;-59.75 to-14.85 Ω). The small and medium TDC probe measures were moderately correlated to spot bioimpedance measurements (r=-0.54 and r=-0.43, respectively). Intra-rater reliability coefficients (ICC2,1) of TDC measures ranged from 0.50 (95% CI: 0.12-0.75) to 0.92 (0.82-0.96). TDC technical error of measurement for women with lymphedema varied from 10.5% to 13.3%. Conclusions: Both TDC and spot bioimpedance may have a role in clinical assessment of tissue compositional change in BCRL. Their relationship with tissue composition, assessed by imaging, is now required.