Abstract: The similarities of The mass spectra of any two isomers (n and m) are represented by a similarity index SI(n, m). The similarity index is calculated using a novel formula: SI(n, m) =minR(n, i), R(m, i) / maxR(n, j), R(m, i) 100 Where R(n, j) and R(m, j) are The intensity ratio of a fragment pair (j); j is an ordinal number which is arbitrarily assigned to a selected pair of fragments. The value of similarity index ranges from 0 to 100, when n = m, The SI(n, m) = 100. Similarity indices of mass spectra of isomeric tetradecadien-1-ols were calculated by The "min.-max." Fuzzy similarity analysis. The universality of The method was confirmed by The testing with mass spectra of ten isomers of tetradecadien-1-ols.