Ambient temperature measurements in a launch vehicle compartment were carried out during flight for two different ISRO missions using two different types of temperature sensors. Despite the same configuration and depressurization rate, differences in measured compartment temperatures were observed in the two flights. Ground tests were carried out simulating flight depressurization rate, to study the effect of sensor mass on ambient temperature measurements. A theoretical heat and mass transfer model was developed for estimating the bulk mean temperature of resident air, subjected to depressurization, during experimental studies. Thermal response analysis of sensors was also carried out to bring out the effect of sensor mass. The need to use fast responding temperature sensors with minimal thermal mass for accurately measuring ambient temperature variation during a transient process such as depressurization is highlighted.