To examine intra- and inter-individual variation of urinary selenium, molybdenum and iodine concentration, a spot sample of morning urine was continuously collected from 12 healthy Japanese young adults (7 males and 5 females) for seven days and selenium, molybdenum and iodine in these urine samples were determined by inductively coupled plasma mass spectrometry. Minimum, mean, median, geometrical mean and maximum values (μg/g creatinine) for the all samples were as follows: selenium, 18, 36, 35, 34 and 72, respectively; molybdenum, 14, 69, 57, 57 and 206, respectively; iodine, 15, 160, 89, 99 and 1105, respectively. Coefficients of variation for the all samples were estimated to be 27.8% for selenium, 83.8% for molybdenum and 118.1% for iodine. Ratios of intra- to inter-variance were calculated as 1.88 for selenium, 2.32 for molybdenum and 2.58 for iodine. These results indicate that the variation of urinary iodine was higher than that of selenium or molybdenum, and the intra-individual variation was higher than the inter-individual variation in urinary selenium, molybdenum and iodine. Based on the logarithmical transformed data, median and 5th to 95th percentile of usual urinary excretion (μg/g creatinine) was estimated to be 37 and 26 to 46 for selenium, 60 and 33 to 110 for molybdenum, and 163 and 31 to 576 for iodine, respectively.