The main objective of the study was to investigate the effects of social media marketing on Consumers buying decision making processes. Specifically an explanatory research design was employed to examine the effects of social media Ads, social media Word of Mouth , users’ presence period on social media, users’ exposure time on social media, users’ number of social media account and users’ level of trust in social media on a consumers buying decision making processes. To achieve the objective of the study, the primary data was collected from a sample 279 students of college of business and economics at Bahir Dar University through questionnaire by applying a convenience sampling techniques. The collected data from sample students were analysed using descriptive statistics such as frequency percentage & mean and inferential statistics such as correlation and multiple regression using SPSS version 23 software package .The study revealed and concluded that Electronic Word of Mouth (E-WOM), Users' Presence Period, Social Media Ads, Users' level of trust and Users' exposure time on social media have a statistically significant and positive influence on a consumers buying decision making processes while users’ number of social media account were not statistical significant factor to determine consumer buying behaviour. Finally the study recommended that marketers should have to; use affiliate marketing, align themselves with other trusted brands, publications & influencers/opinion leaders, keep open and honest communication on social media, offer different benefit such as after sales service to the customer to generate positive word of mouth and should have to use the right combination of video, photo, banners, model and creator of social media that will encourage prospective consumers to purchase.