Choice overload has long been a controversial topic in consumer psychology. While some researchers argue that larger assortment sets benefit consumers, some have argued that large assortments lead to choice overload (i.e. decreased satisfaction). A meta-analysis found that the average effect size for studies supporting the desirability of large assortments was equal to the average effect size for studies finding choice overload. Further, the meta-analysis could account for only 56 percent of the effect size variance, suggesting that there is still significant variance left unexplained. Building on these findings, many scholars have argued for a need to focus on when choice overload occurs, rather than whether it occurs. Consistent with those calls, a number of researchers have since identified moderators, such as option attractiveness, time pressure, product type, construal level etc. Among these factors, also including individual difference moderators. For instance, previous research showed that compared to satisficers, maximizers were more susceptible to choice overload. Additionally, compared to analytic thinking, participants with holistic thinking were less susceptible to choice overload. As an important individual difference variable, we want to know whether regulatory mode can be a boundary condition to moderate the effect of choice overload. Thus, the purpose of the present research is to explore the moderating effect of regulatory mode on choice overload based on regulatory mode theory, by using two different indicators of choice overload, and two manipulating methods of regulatory mode. The present study included two experiments. The first experiment employed 2(regulatory mode: assessment/locomotion) × 2(assortment size: large/small) between subjects design, used RMQ to measure regulatory mode, and took decision regret as dependent variable of choice overload. The participants were asked to complete RMS, and were distributed into large or small size condition, then, they were required to make choices of sweet flavours. The second experiment also employed 2(regulatory mode: assessment/locomotion) × 2(assortment size: large/small) between subjects design, differently, we used priming task to manipulate regulatory mode, and took choice deferral as dependent variable of choice overload. The participants were asked to complete priming task about regulatory mode, and were required to make choices of shoe styles. Results from the first experiment indicated that regulatory mode moderated the relationship between assortment size and decision regret. Specifically, assessors experienced more decision regret in the large rather than small size. In other words, they showed choice overload effect; however, for locomotors, there existed no differences on regret. The second experiment demonstrated that regulatory mode moderated the relationship between assortment size and choice deferral. Specifically, assessors were more inclined to defer their choices in the large rather than small size. In other words, they showed choice overload effect; however, for locomotors, there existed no differences on choice deferral. Further analysis based on mediated moderation showed that decision difficulty played a mediating role in this effect. These results suggested that regulatory mode moderated the effect of choice overload. Regulatory mode appeared to be an important boundary condition of choice overload effects, specifically, compared to locomotors, assessors exhibited choice overload effect. Moreover, based on mediated moderation, we found that decision difficulty could partly explain above effects.