This study aims to assess the quality of mortality data from the registration system of Thailand. The study takes advantage of the Kanchanaburi Project by comparing the deaths found in the annual censuses to those recorded in the civil registration system in order to measure the level of under-registration. The age and sex pattern of death registration found in this study might be useful information in adjusting the data from this source. Moreover, this study also pointed out a possible gap between the multiple steps of death registration, from notifying the death to officially registering it. This finding suggested a hypothesis to be further tested.