In this study, the ratios of monthly sales to the highest monthly sales of listed companies in Taiwan are used to construct the highest monthly sales momentum strategy, which generates significant positive average returns over 1- to 12-month holding periods. The highest monthly sales momentum is a unique effect that persists even after controlling price momentum, 52-week high price momentum, earnings momentum, sales momentum, investor attention, and risk. I also find that investors tend to overreact to good news near the highest sales and underreact to bad news far from the highest sales, so that there is no long-term price reversal in the highest monthly sales momentum.