Abstract Supernova (SN) 2018cow is an optical transient detected in the galaxy CGCG 137–068. It has been classified as an SN due to various characteristics in its optical spectra. The transient is also a bright X-ray source. We present results of the analysis of ∼62 ks of X-ray observations taken with the Neil Gehrels Swift Observatory over 27 d. We found a variable behaviour in the 0.3–10 keV X-ray light curve of SN 2018cow, with variability time-scales of days. The observed X-ray variability could be due to the interaction between the SN ejecta and a non-uniform circumstellar medium, perhaps related to previous mass ejections from a luminous-blue-variable-like progenitor.