One of the trends redefining and reshaping the landscape of the mass media not only in Nigeria, but also globally is the integration of User-Generated Contents (UGCs) in professional journalism practice. This trend which is driven by the social media has engendered citizen and participatory journalism. However, in spite of the seeming contributions of UGCs to the expansion of the public sphere, there are genuine concerns and fears about the erosion of gatekeeping and factual verification of information. To this end, this research is anchored on the Public Sphere Theory and Technological Determinism Theory.  The focus of this study therefore was on User-Generated Contents (UGCs) and professional journalism practice in Nigeria, and how journalists in select media houses in Abuja and Lagos perceived and used this phenomenon.  The research design was survey; the sampling technique was accidental or convenience sampling, while the research instrument was questionnaire. A key finding of the research amongst others was that  Twitter UGCs were the most used, followed by those from YouTube. The authors recommended that while social media UGCs should be used with caution especially in a country like Nigeria where there is gullibility of information-consumption without verification.