Purpose: to evaluate the role of high resolution 20 MHz ultra sound in assessment of posterior segment disorders. Patients and Methods: a prospective, case series study was conducted on 40 patients who attended the ophthalmology outpatient clinic of Al-Azhar university hospitals (2014-2018). All should have a posterior segment disorder either retinal, vascular, vitreo-macular, optic nerve head or choroidal disorder. They should be with clear media, therefor we can reach a diagnosis based on clinical examination and augmented by optical coherence tomography (OCT) and fundus fluorescein angiography (FFA) whenever indicated, the patients were evaluated using both high resolution 20 MHz ultrasound(US) and conventional 12.5 MHz US and compare their results to the gold standard clinical diagnosis to assess their sensitivity to reach the diagnosis. Results & Conclusion: we have two main characters for well diagnosis by any US tool, resolution and sensitivity, and neither the 20 MHz nor 12.5 MHz could combine both of them. Therefore, we recommended tocombine the examination by both of them as they are complementary to each other.