Background <p>Obtaining informed consent is the practice of respect for persons that gives the right to participants to make autonomous decisions about research participation. The difficult-to-read research informed consent forms (RICFs) hinder comprehension and can expose participants to harm. This study aims to assess the readability of health RICFs for studies approved by the National Health Research Ethics Committee (NatHREC) in Tanzania.</p> Methods <p>We used a retrospective cross-sectional study design. A total of 266 RICFs were sampled from the NatHREC database using stratified and systematic random sampling strategies. The readability of RICFs was assessed using the Flesch Reading Ease (FRE) and Flesch-Kincaid Readability Grade Level (FKRGL) formulas available in Microsoft Word Office and by manual check. Data were collected using the assessment checklist, analyzed, and presented with SPSS and MS Excel software.</p> Results <p>Out of 266 RICFs assessed, 65.4% had the recommended page numbers, 81.6% had longer sentences, and 80.5% were difficult to read, necessitating a person to acquire a US grade 10 (Form Four educational level in Tanzania) to understand the presented information. Pearson’s correlation coefficient with p-values of &lt; 0.001 and 95% confidence level disclosed that sentence lengths in the RICFs had a statistical association with the difficult reading levels obtained.</p> Conclusion <p>Findings from this study showed that most of the RICFs were concise in terms of page numbers and word count but had long and difficult sentences. Researchers should assess the readability of RICFs before submitting them for ethical approval. Research Ethics Committees (RECs) should consider inclusion of RICFs readability measurements in the Ethics Guidelines for Health Research. The study recommends further studies to assess the Kiswahili versions of RICFs to determine if the results obtained in this study apply to Kiswahili texts.</p> Clinical trial number <p>Not applicable.</p>