We present time-series imaging polarimetry observations of a very nearby superluminous supernova 2018hti at z = 0.063, to probe its explosion mechanism and shed light on the energy source powering superluminous supernovae (SLSNe). We obtain linear polarimetry using the Alhambra Faint Object Spectrograph and Camera on board the 2.5 m Nordic Optical Telescope. Our observations show polarization at the ̃1.9% level before and after the supernova reached light-curve maximum. However, this level of polarization is consistent with the line-of-sight interstellar polarization; hence, the polarization from the supernovae itself was not detected at a level of >3σ. This suggests that the explosion of SN 2018hti is almost spherical, similar to previous polarimetry studies of other SLSNe.