An electric connecting structure comprising preferred oriented Cu6Sn5 grains and a method for fabricating the same are disclosed. The method of the present invention comprises steps: (A) providing a first substrate; (B) forming a first nano-twinned copper layer on part of a surface of the first substrate; (C) using a solder to connect the first substrate with a second substrate having a second electrical pad, in which the second electrical pad comprises a second nano-twinned copper layer, and the solder locates between the first nano-twinned copper layer and the second nano-twinned copper layer; and (D) reflowing at the temperature of 200° C. to 300° C. to transform at least part of the solder into an intermetallic compound (IMC) layer, in which the IMC layer comprises plural Cu6Sn5 grains with a preferred orientation; wherein at least 50% in volume of the first and second nano-twinned copper layer comprises plural grains.