The historical large earthquakes in 1797 and 1833 accompanied by tsunami struck the Mentawai region and some cities in southern part of Sumatra. We conducted tsunami modeling referring source models of the two earthquakes from the previous study of coral micro atoll along the Mentawai islands. Tsunami numerical simulation code used in this study is TUNAMI-N2 with the nested grid system by adopting nonlinear shallow water theory. Five source models based on the 1797 and 1833 earthquakes were simulated for the tsunami hazard assessment, which include three original source models (Cases 1, 2a and 3a) from the coral studies and two source models (Cases 2b and 3b) introduced in this study considering energy reduction after the 2007 Bengkulu and 2010 Mentawai earthquakes. Tsunami simulation produced the highest data values of maximum tsunami height of 7.3 m and tsunami inundation depth of 7.2 in Muko-muko region for Case 1 (1833, Mw 8.9). In Padang for Case 1, the calculated tsunami inundation depth was 1.95 m at the tide gauge station, 3.7 m at Teluk Bayur Port, and 3.8 m at Teluk Bungus beach. The maximum run-up height was about 4 m, which reasonably explains the historical tsunami run-up height data of 3.0 - 4.5 m in Padang. In Muko-muko the maximum tsunami height was 6.1 m and tsunami inundation depth was 6.0 m for Case 2a. The maximum tsunami run-up height in Case 3a (1797, Mw 8.7) was 2.8 m, which is slightly smaller than the historical data of about 5 m in Padang. Using the modified source models, which may correspond to future earthquake scenarios, the maximum tsunami heights were about 5 m in Baganti for Case 2b (1833, Mw 8.2) and about 2 m in Pariaman for Case 3b (1797, Mw 8.5), respectively. The simulation results from Case 2b and Case 3b may be regarded as more realistic scenarios of tsunami event.