The objective of this research is to understand the effect of micro-influencer on follower on Instagram in Thailand by investigating the effect of different level number of followers of a micro-influencer and product involvement with the relationship between perceived expertise of micro-influencer on brand trust and purchase intention. This study used a quantitative method and was implemented though online questionnaire, 300 valid response were collected within 2 months. The measurement were adapted measurement scale from (Ohanian, 1990) and (Zaichkowsky, 1985) in order to measure variables.
The result of this study shows that perceived expertise of micro-influencer can enhance the purchase intention and brand trust. In terms of follower base of a micro-influencer, it is verified that high number of followers have more impact on purchase intention than micro-influencer that has low and medium level of followers. However, higher follower base of a micro-influencer does not have positive effect on the relationship between expertise and brand trust. product involvement has the positive direct both intention and brand trust but there is no significant effect on the relationship between perceived expertise and purchase intention as well as on brand trust.

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