Impulsive behavior among Indonesians, particularly among members of generation Y, has been attributed to the rise of online purchasing. Consumer impulsivity has the potential to become a prospective market segment, allowing e-commerce to generate promotional activities such as flash sales to drive shoppers' propensity toward an impulsive purchase behavior. This research aims to prove the effect of flash sales on online impulse buying mediated by positive Emotions on generation Y. This research employed causal research design as part of used quantitative research methods. The questionnaire was distributed to a total of 205 people who fulfilled the purposive sampling criteria as Shopee users in the generation Y category. Data were analyzed using the Structural Equation Model (SEM) with the AMOS 26 program. The findings revealed that flash sales and positive emotions significantly affect generation Y's online impulse buying behavior at Shopee, and positive emotions mediate this effect.