Abstract Background The expression of estrogen receptor beta (ER beta) and its correlation with the prognosis of malignant mesothelioma remains controversial. This study aimed at studying ER beta expression in tumour cells in patients with mesothelioma and its association with clinicopathological factors and survival outcomes. Material and Methods A prospective study to evaluate prognostic significance of ER beta overexpression by immunohistochemistry (IHC) on paraffin blocks among malignant mesothelioma patients at Ain Shams university hospital and correlate their overexpression with the patients' follow up clinical data, OS, and PFS. Results Forty-two mesothelioma cases were enrolled and followed up, High ER beta expression (modified Allred score 7-9) was reported in 9.5% of the patients (4 cases), moderate expression (modified Allred score 4-6) was reported in 28.6% of the patients(12 cases), weak and negative expression ( modified Allred score 0-3) was reported in 61% of the patients(26 cases), percent of ER beta positive cases was 69% of the total patients, there was no statistical difference as regard age (p value:0.8), sex(p value:0.4), stage (p-value: 0.71), ECOG (p-value :0.84), histological subtype(p value:0.17) and response to first-line treatment (p value:0.5) across the 3 groups of patients (high, moderate, weak and negative ER beta on tumour cells).there was no statistically significant difference in OS and PFS for ER beta overexpression. Conclusion ER beta overexpression was not associated with improved OS or PFS in mesothelioma patients, larger sample size would be recommended for more solid conclusions.