The research study aimed to explore the sociolinguistic function of the register used on Instagram captions such as intimate, deliberative, casual, oratorical/ frozen, and consultative functions. The researcher adopted a qualitative method approach to analyze the data. The theoretical framework of this research is based on Halliday’s (1978) model of register. The study at hand finds the intimate function of the register 27 times, deliberative 19 times, causal 7 times, oratorical 3 times, and consultative 35 times. Moreover, the present study analyzed that majority of the Pakistani influencers have used informal registers. Therefore, suggesting that influencer in web-based media, particularly Instagram captions, use various types of registers in a variety of settings, as well as slang, contractions, and vernacular language. The purpose of using slang language is to increase the viewers’ reading speed and casual register-based content makes the audience comprehend easily. It is crucial for an influencer to be aware of the type of register he or she is using. If an influencer understands the application and function of register in Instagram captions, s/he can market his or her advertisement with ease.