Provided in the embodiment of the present invention are a memory card authentication method and a mobile terminal thereof, and a terminal device. The authentication method comprises: the mobile terminal performing an identification information detection on a memory card connected thereto to obtain a nominal memory capacity of the memory card; the mobile terminal filling the memory card with a predetermined amount of data and judging whether the predetermined amount and the nominal memory capacity of the memory card meet a predetermined condition; and determining that the nominal memory capacity of the memory card is correct when the predetermined condition is met. According to the present application, an identification information detection is performed on a memory card to obtain a nominal memory capacity of the memory card and the memory card is then filled with a predetermined amount of data, an actual memory capacity of the memory card is determined by judging whether the predetermined amount of data fille
