Measurement of radionuclides concentration in foodstuffs allows to assess the intake’s assimilated dose. This contributes at least one-eighth of the mean annual effective dose due to natural sources. Among the trace elements in foodstuff, potassium is one of the most important elements. It is a well-known essential element and it occurs all over the earth. Three of the most customary consumed foodstuffs in Mexico since pre-Hispanic time (by all social classes) are the following: bean, chili and corn meal (“tortillas”). They were analyzed by γ-spectrometry in order to determine 40K activity concentration, the derived annual effective dose, and the K mass fraction (%). Results show that the mean activity concentration of 40K, annual effective dose and K mass fraction (%) are as follow: 901 ± 90 Bq kg−1, 37.2 ± 3.7 μSv a−1 and 2.84 ± 0.27 % for chili; 510 ± 10 Bq kg−1, 27.5 ± 0.5 μSv a−1 and 1.60 ± 0.04 % for bean; and, 90 ± 30 Bq kg−1, 58.1 ± 19.4 μSv a−1 and 0.27 ± 0.089 % for corn meal, “masa”. The total effective dose intake from these typical foodstuffs is about 0.122 ± 15.6 mSv a−1in Mexico’s urban zones.