This study presents the energy harvesting characterization of piezoelectric ceramics Lithium Niobate (LNB) and Lead Zirconate Titanate (PZT). PZT and LNB have been used for sensing and energy harvesting applications in the past due to its high piezoelectric and pyroelectric coupling coefficient in the case of PZT and high Curie temperature in the case of LNB. However, characterization of power output of these materials under different thermal and mechanical loads has not been performed in depth. In this study, power output of LNB at different electrical loads due to several thermal stresses was measured. These thermal stresses were introduced using a custom testing setup. In addition, a custom testing setup was fabricated to characterize the response of PZT under thermal and mechanical loads combined. LNB was tested at three different temperature ranges. Pyroelectric coefficient of LNB, as well as peak power at these ranges is reported. Furthermore, PZT was tested under pure mechanical, pure thermal, and combined loads. Power response from the PZT sample was measured using a varying electrical resistance to find the optimum load and its correlation to the testing conditions. Pyroelectric coefficient of LNB was found to increase when temperature was incremented, with a maximum value of -196 μC.m-2°C-1 at the 200°C to 225°C. However, it was observed that power decreases as higher temperatures are introduced. A peak power density of 111.84 nW/cm3 was found at the 200 °C to 225 °C temperature range. Finally, the introduction of combined thermal and mechanical loads to the PZT sample yielded overall higher power outputs compared to when only one of these loads was introduced. These results provide a better insight of electrical power generation by piezoelectric ceramics under different thermal and mechanical loads for energy harvesting applications.