Alloy beams and beam like elements are principal constituents of many structures and widely used in high speed machinery, aircraft and light weight structures. Crack is a damage that often occurs on members of structures and may cause serious failures of structures. In this research the natural frequency of a cracked cantilever beam is investigated by finite element method by using of ANSYS program with different crack depth and location effect. The beam material studied is aluminum alloy, titanium alloy, copper alloy and magnesium alloy. A comparison is made between these alloys and conclude optimized result between them. The increase of the beam length result in a decrease in the natural frequencies of the composite beam and also shows that an increase of the depth of cracks lead to a decrease in the value of natural frequencies.