The study examines the effects of electronic word-of-mouth (message quantity and message appeals) on purchase in social network sites. Message quantity (many and few) and message appeals (rational and emotional) are manipulated in a 2×2 factorial experiment. Product involvement and trait of buying impulse as moderator. In the sta-tistical method, this study utilizes independent sample t test and two-way ANOVA to test the hypotheses. The finding of the study are as following: the more of message quantity, the greater influential it is on consumer’s purchase intention and consumer prefer the messages of rational. Product involvement has a negative correlation with message quantity, the lower involvement is, the higher influence of the message quan-tity on the purchase intention is. And trait of buying impulse also has a negative corre-lation with message quantity, the lower trait of buying impulse is, the higher influence of the message quantity on the purchase intention is.
