Desorption of gold ions from liver tissue sections, in which intravenously injected gold nanorods were accumulated, were studied to evaluate properties of gold nanorods as a "mass-tag". Gold ions were sensitively detected by using a conventional MALDI-MS machine. When 50-µm-thick blank sections without gold nanorods were placed on or beneath a sample section, desorption of gold ions was almost suppressed. It was found that the escape depth of gold ions from liver tissue sections was less than 50 µm. It was found that we do not have to take account of the escape depth of gold ions if a section were sliced into 10-20 µm thickness.