This study developed a regression model to explain variations in advertising intensity among firms within the same industry and compared the explanatory and predictive power of this model with existing advertising intensity models. Analysis using time-series cross-sectional data covering 153 firms across 23 domestic industries over the most recent six years revealed that the model developed in this paper explained an average of 75 percent of the variation, demonstrating substantially higher explanatory power than existing models, including the recently developed model by Balasubramanian and Kumar (1990). In particular, this model showed that in a considerable number of industries, the previous year's advertising intensity was maintained in the following year. However, the predictive power of this model with such high explanatory power was found to be virtually no different from that of the extremely simple five-year average model (i.e., the average of advertising intensity over the past five years).