BackgroundThere are large gaps in health and well-being among different groups of the society. Socioeconomic factors play a significant role in determining the health status of the society. The present study was conducted to examine socioeconomic inequality in health status among the adult population of Khorramabad city, the capital of Lorestan province, wester part of Iran.MethodsA cross-sectional study was conducted on 1348 participants selected through multistage sampling. A valid and reliable questionnaire was used for data collection. The wealth index as an indicator of the socioeconomic status (SES) was used to categorize the subjects in terms of the SES. The concentration index and concentration curve was used to measure socioeconomic inequity in poor self-rated health (SRH) of population. Finally, after determine the status of inequity in poor SRH, a decomposition analysis approach was used to identify the most important determinants of this inequity.ResultsThe prevalence of poor SRH was 18.91% in all subjects, 38.52% in the lowest SES group, and 11.15% in the highest SES group. The value of the concentration index for poor SRH was − 0.3243 (95% CI − 0.3996 to − 0.2490), indicating that poor SRH was more concentrated among the poor. The results of decomposition analysis showed that SES (41.2%), higher body mass index (28.6%) and lack of physical activity (26.9%) were the most important factors associated with the concentration of poor SRH in the poor groups.ConclusionIdentification of socioeconomic factors affecting on health status is the first step for proper policymaking. Policymakers and health system managers at the national and subnational levels can use the results of this study as well as other similar domestic studies to design and implement proper interventions to promote equity and improve the health status of population.