The scientific journal is an important part of scholarly communication and for a long time it has functioned both as the sole dissemination channel of research findings and as an important indicator of research quality. Recently altmetrics have been investigated for their applicability for research assessment. The potential of and hope attached to altmetrics is that they could function as complements to more traditional metrics and possibly reflect some aspects of new forms of online scholarly communication. This research will investigate aggregation of altmetrics at journal-level and the online presence and visibility of selected Korea-based journals. Based on our findings we can conclude that Open Access availability is a clear driver for higher online attention for Korean scientific journals, however, this attention is also heavily influenced by the popularity of a few articles that have attracted significant online attention. Because of the influence some popular articles can have on the aggregated journal-level attention, journal-level altmetrics do not appear to be reliable nor useful indicators of the performance of scientific journals. © 2018, Akadémiai Kiadó, Budapest, Hungary.