Since its rapid growth within, Word of Mouth occurs all the time with Social Media. Social Media defined to be genuine conversation of people in mutual interest. Word of Mouth in the business is vocal aspect in brand and marketing. One of outcomes in Social Media is Word of Mouth in which affected between is Brand Engagement. Research conducted with random sampling on AirAsia social media liker or follower. Method that been used are R2, T-test and Path Analysis. Research results show significant effect on Social Media Participation and Engagement on Brand Engagement. The result also shows significant effect on the Brand Engagement on Word of Mouth. Social Media and Word of Mouth does not have indirect effect, which can be explained by result of .295 > .380 is not correct. The results shows Social Media Participation has strong relationship on Brand Engagement which explained by .652 of R2 value, while Brand Engagement has moderate relationship on Word of Mouth which explained by .452 of R2