6 mm thick and 1500 mm wide magnesium alloy AZ91 sheet was produced by twin roll casting. Sheets were homogenized between 350-475 degrees C for 1-24 h. Afterwards, they were warm rolled down to 2.75 mm. Age hardening was also performed on twin roll cast AZ91 alloy sheets. Specimens were aged at 150, 200 and 250 degrees C for up to 100 h. Characterization was performed by light microscope, TEM-EDS, and XRD after twin roll casting and also after each thermomechanical process including aging. Tensile tests were performed for mechanical properties. Moreover, the age-hardening response of Mg AZ91 alloy was examined by micro hardness test.