Deformation twinnings in magnesium activated on the c-axis compression were investigated by light and electron transmission microscopies. Well-known twin forms of {1013} and {3034} habit planes were confirmed again, but {1013} twins were frequently observed to occur in groups along {3034} or grow from {1013} habit to {3034} habit. Transmission electron microscopic observations revealed that the well-developed {3034} habit twin has the same orientation relationship with the parent crystal as the {1013} twin. From these observations, it is concluded that the well-developed {3034} habit twins are the {1013} twins developed along {3034} planes. A possible mechanism of the habit plane change is described and the relation between the twin and the compression band is discussed
