Background and objective: The introduction of immune checkpoint inhibitors (ICIs) in oncology presents a critical healthcare policy challenge for resource allocation due to their substantial financial burden. This study assessed the reporting quality of health economic evaluation (HEE) studies of ICIs. Methods: This study conducted a systematic literature search of four databases (PubMed, EMBASE, Cochrane CENTRAL, and the International HTA Database) for studies published between January 1, 2014 and December 31, 2022. All ICIs approved up to December 31, 2022, in the USA, EU, China, and Japan were included. Reporting quality was assessed using the Consolidated Health Economic Evaluation Reporting Standards published in 2013 (CHEERS 2013), which is the most widely recognised and implemented reporting guideline for HEE studies. Subgroup analyses were also performed based on the risk of sponsorship bias or citation of CHEERS 2013. Results: A total of 5368 records were identified, 252 of which were included after full-text review. The study design, setting, and ICIs most frequently observed were cost-effectiveness and cost-utility analyses (63.5%), the USA (46.0%), and pembrolizumab (38.1%), respectively. Of the 24 items of CHEERS 2013, fully reported items were limited, particularly in the Methods section. Setting and location were not reported in 94.4% of the records. Subgroup analyses also revealed insufficient reporting of items in the Methods section, particularly "Setting and location". Conclusion: Health economic evaluation studies on ICIs between 2014 and 2022 had limited reporting across the 24 items of CHEERS 2013, regardless of sponsorship bias risk or citations. The items on setting and location in the Methods section were particularly underreported, emphasising the need for transparent reporting in HEE studies of ICIs.