Instagram as one of the famous social network sites in this century is as one way to share various kinds of general information and to present our activities, events, achievements, vacations, and so forth. The present study explored expositive acts presented in the caption of Instagram-posting by Indonesian users. It is interesting that expositive acts used are to emphasize self-presentation on their posting. 734 photo-posting with caption from 15 participants were found. The expositive acts performed by the participants were classified based on the kinds of expositive acts as proposed by Austin (1962). The factors initiating each kind of expositive acts were described. The representation of self-presentation on expositive acts was discussed. The present study found ten kinds of expositive acts which were also identified as the communicative intention presented in their Intagram-posting with caption, namely: apprising, describing, affirming, supposing, remarking, informing, postulating, confirming, arguing, and telling. Finally, the present study offer implication for further study that the caption used in this social medium is as another valuable aspect in Instagram for emphasizing self-presentation phenomena, in which this caption is also incorporated with communicative intention by the users implicitly or explicitly addressed to others.