People are aware that outdoor air pollution is harmful to their health, but indoor air pollution can also cause serious health complications. This study aims to determine the indoor air quality of modernized jeepneys to identify the best solutions to eliminate harmful emissions and provide comfort and good health for the occupants. The researchers conducted an IAQ assessment, including the following concentrations: carbon dioxide, carbon monoxide, PM₁₀, PM_2.5, formaldehyde, temperature, and relative humidity. In addition, a correlation of the parameters with the number of passengers and the cycle of opening-closing of the door were identified. A survey was conducted to explain the sampling results further. Based on the results, PM_2.5 and PM₁₀ were the only contaminants that appeared to be within the standards. Temperature and carbon dioxide both have a relationship with the number of passengers. Carbon dioxide and PM_2.5 both have a relationship with the cycle of opening-closing of the door. The rest of the results and recommendations drawn based on these results are discussed in the latter part of this paper.