In recent years, there has been an increasing call for more public engagement of scientists, and this happens in parallel with a rising internationalization of research. Willingness to communicate is explained by attitudes (ideas and perceptions about science communication), but is also the result of a combination of personal and contextual factors. Disciplinary cultures have been pointed out as important factors in explaining communication practices. Our hypothesis is that the way scientists view and engage in science communication is related to their scientific discipline, but also to a participation in international networks. The internationalization of scientists has been found to impact their human capital, which is constituted also by ideas and beliefs, which are also related to science communication. A survey was responded by 524 researchers from nine Portuguese scientific institutions and research groups. We found that disciplinary cultures are relevant factors to explain differences in the perceptions about science communication and reasons to communicate, namely those related to extrinsic motivations. Disciplinary cultures were also found to mediate the impact of internationalization on ideas about science communication. Internationalization in the whole group of researchers was found to be positively associated with communication practices targeting different audiences.