Disclosed is a negative active material showing small change in volume during charge/discharge cycle enabling less electrical insulation, and having excellent initial efficiency and an excellent capacity maintenance characteristic. Lithium can be more easily diffused in the material thanks to the existence of a fine crystalline region in a matrix of an alloy. More specifically, the present invention provides a negative active material for a secondary battery, the material having the formula SixTiyFezALu (x, y, z, and u are at%, x is 1-y+z+u) and ranges from 60 to 70%, y is from 9 to 14%, z is from 9 to 14%, and u is larger than 1 % but less than 20%) and an amorphization degree on a matrix within an alloy of 25% or more. The negative active material has an improved expansion rate of 70 to 150% after 50 cycles.