Purpose: To investigate skin dose dosimetry of postmastectomy electron radiotherapy (RT) with the use of patient-tailored three-dimensional printed bolus (3DPTB) and Pinnacle 3D electron beam calculation.Methods and Materials: We evaluated the dosimetric parameters and percent depth dose (PDD) with the use of 3DPTBs in both in-vivo patient study and phantom measurements. For the in-vivo study, 20 patients were enrolled and 3DPTB was designed for each patient based on the computed tomography (CT) simulation image. The skin dose was measured using EBT3 film and was compared to the treatment planning system (TPS) calculated dose for each measurement. Effect of applying gel in skin dosimetry was also investigated in the in-vivo study. For the Phantom study, we used torso phantom and EBT3 film. PDD curves for the measured dose and the TPS calculated dose by energy (6 MeV vs. 9 MeV) and bolus thickness (0 cm, 0.5 cm, 1 cm, 1.5 cm and 2 cm) were generated to evaluate the accuracy of TPS calculation. Results: In in-vivo patient measurements, mean dose to the heart and lung in current study was 1.98 Gy and 8.39 Gy respectively. When 2 patients with Rt breast cancer were excluded, mean dose to the heart and lung in current study was 2.11 Gy and 8.51 Gy respectively. The average of the % difference was -2.3 % (range, -16.5 % - 8.5 %) and was decreased to -0.8 % (range, -12.0 %- 14.8 %) with the use of gel between chest wall and bolus. In general, the increase in bolus thickness was associated with greater discrepancy between the measured vs. calculated dose. In the phantom study, when applying the boluses with thickness < 1 cm and ≥ 1.5 cm, the use of 6 MeV and 9 MeV energy could minimize the discrepancy between measured vs. calculated doses, respectively. Conclusion: Current study shows that electron PMRT using 3DPTB with PLA bolus material and Pinnacle TPS can be applied to clinical practice when accepting approximately 8 % of discrepancy between planned dose and actual dose delivered to the skin in selected patients. This discrepancy can be decreased to approximately 5 % with the use of gel. Bolus thickness of < 1 cm and ≥ 1.5 cm are recommended to be used with electron energy of 6 MeV and 9 MeV, respectively to minimize the discrepancy between planned and measured skin dose base on the phantom study.