Surface modification is deemed as a reliable strategy to regulate the photocatalytic properties of a bare photocatalyst. In this work, multiwall carbon nanotubes (MWCNTs) decorated BiOCl composites were successfully in-situ fabricated via a hydrothermal routine and studied by a series of methods. The results demonstrate that a strong chemical interaction forms between MWCNTs and BiOCl, supported by data from XRD, Raman and XPS experiments. The photocatalytic activities of the MWCNTs/BiOCl materials were tested under UV light irradiation using phenol as a model molecule. The results reveal that adding relatively low amounts of MWCNTs can ameliorate the photocatalytic activity of BiOCl. Among them, the 3% sample exhibits the best activity towards degradation of phenol. The enhancement in photocatalytic performance can be tightly ascribed to the enhanced separation rate of the photoinduced carriers, in accord with the surface photovoltage spectroscopy (SPS) investigation. MWCNTs facilitate the effective formation of O-2 center dot(-), resulting in rapid decay of phenol over the MWCNTs/BiOCl materials. In view of all the obtained experimental results, a photocatalytic enhancement mechanism for the MWCNTs/BiOCl composite is presented.