Instrumental neutron activation analysis (INAA) is one of the high metrological techniques for mineral determination. Nevertheless, it has some limitations for minerals with low detection limits, such as lead and cadmium, for which graphite furnace atomic absorption spectrophotometry (GF-AAS) provides reliable outcomes. This study was conducted to determine nutrients and toxic elements in four varieties of rice and six varieties of legumes. Rice and legume samples were collected from Talad-Thai and Yoawarat markets, which were representatives of rural and Bangkok areas, respectively. INAA was used for determination of various minerals whereas GF-AAS was used to determine Cd and Pb. In-house reference materials (RMs: white jasmine rice and soybeans) were prepared and their mineral contents were assigned, along with certified reference materials, by INAA and GF-AAS with standard addition technique. The INAA and GF-AAS methods were validated by various certified reference materials which showed a fairly good accuracy, 0.7–4.5% bias for INAA; 1.54 and 6.06% bias for AAS. The precision of INAA and GF-AAS, relative standard deviation (RSD) of all studied minerals was good (RSD less than 8.9%).