Measuring socioeconomic status (SES) is very important in educational research, as researchers often use this information to contextualize the results of an assessment or to control for SES when analyzing the relationship between academic achievement and other variables. However, any cross-country comparisons using SES data from international large-scale assessments, such as the Programme for International Student Assessment (PISA), should be preceded by a careful examination of the psychometric properties of the scale used to measure SES, an issue which is rarely addressed by researchers. The current study aims to fill the gaps in this field of research by analyzing the longitudinal and cross-country measurement invariance of the PISA home possessions scale, a 25-item scale which measures household wealth, one of the three components used to measure SES in PISA. Using multiple group concurrent calibration with partial invariance constraints, the study found that four items in the scale, all related to technology, functioned differently across the PISA cycles. It also found that some items (i.e., bathroom, classic literature, poetry books, and TV) functioned differently across the participating countries when used to measure family wealth. The overall level of misfit found in the scale was not associated with the country’s GDP per capita, while some evidence suggested that it may be associated with the region in which the country was located and sociocultural factors (which were partially captured by the language in which students took the assessment). Compared to the original home possessions scores obtained from the public dataset, the new home possessions scores generated with the method used in the study were found to be a more comparable measure of SES across countries, while the accuracy of the scores as a measure of SES within countries was improved in most cycles. The study also found validity evidence supporting the use of the new home possessions scores as a measure of SES. The results of this study can help improve the PISA home possessions scale, so it can continue to provide valuable information to researchers and policy makers on SES over the PISA cycles and across the countries that participate in PISA.