Abstract: The Earth’s outer radiation belt contains a large number of relativistic (> 500 keV) electrons, which can exhibit different pitch angle distributions (PADs). Whistler-mode chorus waves are considered an important factor governing the evolution of electron PADs, but their long-term and global effects remain insufficiently studied. This paper presents a statistical analysis using observations from the Van Allen Probes during 2013−2018. A pitch angle anisotropy index A is employed to characterize electron PADs, and its correlation with chorus waves is investigated. Statistical results show that when chorus waves intensify, the index A increases, implying that electrons tend to exhibit pancake PADs. In addition, the index A is found to be positively correlated with enhanced solar wind dynamic pressure or substorm activity. Our results demonstrate that chorus waves play an important role in accelerating relativistic electrons and reshaping their PADs, which contributes to a deeper insight into the physical mechanisms underlying the dynamic evolution of the outer radiation belt.