The Mn/Fe ratio in ferromanganese nodules is determined by calibration-free laser-induced breakdown spectroscopy based on the use of only the plasma temperature and electron density and the intensities of manganese and iron analytical lines (Mn I at 447.28 and 447.93 nm and Fe I at 447.65 nm). The plasma temperature was determined by the two-line method (Mn I at 447.28 and 447.93 nm), while the plasma electron density was determined by the Stark broadening of the Mg I line at 517.26 nm. The study was performed using both standard samples (OOPE series) and samples of ferromanganese nodules sampled during expeditions to the Kara and Laptev Seas. The possibility of semiquantitative determination of the Mn/Fe ratio within the range from 0.2 to 4.2, which is enough for determining this ratio in most types of nodules of different geographical origins, is demonstrated. The calibration-free analysis data correlate with the results of inductively coupled plasma atomic emission analysis.