Irreproducibility of preclinical biomedical research has gained recent attention. To improve the quality and transparency of scientific reporting, some journals introduced checklists requiring authors to complete at the time of manuscript submission. Whether a checklist enhances data and reporting quality of preclinical animal studies, however, has not been empirically studied. In this publication, Han et al. searched two highly cited life science journals, one that requires a checklist at submission (Nature) and one that does not (Cell), to identify in vivo animal studies. After screening 943 articles, a total of 80 articles were identified in 2013 (pre-checklist) and 2015 (post-checklist), and included for the detailed evaluation of reporting methodological and analytical information. The authors found that reporting of randomization, blinding, and sample-size estimation significantly improved when comparing Nature to Cell from 2013 to 2015, likely due to implementation of a checklist. Specifically, improvement in reporting of the methodological information was at least three times greater when a mandatory checklist was implemented than when it was not. Reporting the sex of animals and the number of independent experiments performed also improved from 2013 to 2015, likely from factors not related to a checklist. The authors concluded that completing a checklist at manuscript submission is associated with improved reporting of key methodological information in preclinical animal studies.