Our analysis and estimation of R 0 rely on the accuracy of the SI of 2019-nCoV, which remains unknown as of January 25. In this work, we employed the SIs of SARS and MERS as approximations to that of 2019-nCoV. The determination of SI requires knowledge of the chain of disease transmission that needs a sufficient number of patient samples and periods of time for follow-up (Cowling et al., 2009), and thus this is unlikely to be achieved shortly. However, using SIs of SARS and MERS as approximation could provide an insight to the transmission potential of 2019-nCoV at the early stage of the outbreak. We reported that the mean R 0 of 2019-nCoV is likely to be from 2.24 (8-fold) to 3.58 (2-fold), and it is largely in the range of those of SARS, i.e., 2-5 (Bauch et al., 2005, Lipsitch et al., 2003, Wallinga and Teunis, 2004), and MERS, i.e., 2.7-3.9 (Lin et al., 2018).