News consumption via web portals is rapidly increasing in Korea. Web portals do not directly produce their news contents, but select, assign and post them, much like conventional media outlets. Then, do news web portals present similar political bias? To answer this question, this study conducted a big data analysis to objectively measure the political orientation of Korea’s major portals. Firstly, data was compiled on the expressions used by conservatives and progressives in official statements to address certain issues. Next, the relative frequency of these expressions and their significance was applied to measure the political orientation of portals. The results reveal that, web portals are not systematically biased in their selection of contents, but rather, swayed by public opinion. Specifically, profit in the web portal market is generated by the number of user clicks. As such, web portals are highly likely to select news contents that cater to the political leanings of their user base than the government or news providers. How does the political preference of users affect portals’ selection of news contents? Using data on consumer’s click rate and portal’s political orientation, an empirical analysis found that users favored portals that are closer to their political standing, and this in turn, determined the leanings of the respective portals. The results further revealed that this is an inevitable consequence of the afore mentioned incentive structure. Then, are there any related problems with portal’s behavior? Recently in Korea, local portals are expanding their algorithm-based news feed services. However, this raises concerns and a cautious approach is needed. This is because such customized services will most likely reduce the opportunity for users to come into contact with diverse news and perspectives. Additionally, they could polarize public opinion and provide a basis to further disseminate fake news. [Interview] The Korean peoples’ trust in major conventional media is eroding. In contrast, we are also seeing a huge surge in the use of social media, including Facebook and Kakao Talk. As a consequence, more people are sharing and circulating contents within a certain homeogenous group, which makes the polarization of public opinion more inevitable. Worse still, fake news may even become credible. This was evident during last year’s presidential elections in the US. A clear distinction between Korea and the US, in terms of new consumption, is that the share of portal news is high. This means that, even with the growing influence of social media, portals can play a major role in exposing consumers to the diversity of news. And to uphold this diversity, we must reinforce and highlight the editorial rights and the responsibility of portals.