This study was designed to ascertain the level of influence of advertising on the purchase decision of social media users in the Chennai metropolitan area. The sample size was calculated and a total of 151 respondents were selected using a convenience sampling technique. The data were collected using a questionnaire comprising multiple-choice questions and statements to be rated on a five-point Likert scale. Data analysis involved percentage calculation, chi-square, Pearson correlation, and simple linear regression analysis. This study found out that 67% of the respondents purchase products online after seeing an advertisement on social media, whereas 70% like to read reviews before buying merchandise. Moreover, 35% of the respondents identified brand image as the vital component in buying decisions, and 32% selected product quality as the essential element. In addition, 36% of the respondents said that they are influenced by influencer promotions to purchase products. The overall mean score for the respondents’ perception about advertisement was 2.79 on a five-point Likert scale, whereas respondents’ attitude towards the purchase decision, was 2.99. The overall perception about advertisement significantly predicted the frequency of purchases, χ2(4)=11.55, p=.021, and was moderately correlated with the purchase decision (r=.585, p<.001). Similarly, a simple linear regression analysis demonstrated that advertising perception significantly predicted the impact on purchase decisions as described by a 34.2% variance (R-squared=.342, p<.001). The study found out that the influence of advertisement on purchase decisions was moderate. However, the study recommends that social media marketers should try to make advertisements catchy and engaging by considering customers’ preferences and utilizing testimonial ads.