Abstract: In recent years, numerous simulation softwares have been created, upgraded and being used for building thermal performance. Integrated Environmental Solutions-Visual Environment (IES-VE) is considered as one of the common thermal performance simulation programs. This study discusses the investigation on the accuracy of IES-VE Software in simulating indoor thermal environment of a double-story house in Bangi, Malaysia by comparing with on-field measurement. Air temperature, relative humidity and mean radiant temperature have been selected as the main variables to assess the thermal environment. The on-field measurements were carried out by using ΔΩHD323 WBGT-PMV (indoor measurement) and MK-III Weather Stations™ (outdoor measurement). The results reveal that the differences between the on-field and simulation measurements were in the acceptable range which is 10-20%. Therefore, the simulated data are valid and accurate for further thermal performance prognosis study for the tested building. The results in this study also agree well with those of other researchers.