After the Fukushima Daiichi Nuclear Power Plant (FNPP) accident, maintaining the safety of agricultural products in the event of radiation accidents has become a major social concern. In order to predict the transfer of radioactive materials to dairy products and minimize the spread of contamination to food, we conducted tests in which cattle were fed feed containing relatively low levels of radioactive cesium (134Cs + 137Cs) derived from the FNPP accident. This study consists of two parts: (1) determination of the transfer of radioactive Cs to milk, and (2) measurement of radioactive Cs contamination in tissues corresponding to edible beef in cattle prior to slaughter. Radioactive Cs concentration in milk rose within 1 day after feeding contaminated feed and began to decrease witin 1 day after switching to uncontaminated feed, but it took 4–8 weeks to fall below detection limits. Fecal excretion showed changes similar to those in milk. After even 1 week of continuous feeding of contaminated food, accumulation of radioactive Cs was observed in organs and muscles. We have established a method to estimate radioactive Cs concentration in skeletal muscles using radioactivity values measured by placing the probe of a sodium iodide (NaI) survey meter in close contact with the body surface of live cattle (external measurement). A strong positive correlation between the external measurement (cps) and radioactive Cs concentration (Bq/kg) in slaughtered beef was verified even below 50 Bq/kg.