Temperature-dependent FTIR spectra of linoleic acid were measured over a temperature range of -80 to -30 degrees C to explore solid-state low-temperature (LT) -> middle-temperature (MT) phase transition of linoleic acid. Band assignments were made mainly for the 900-760 cm(-1) region, where the bands due to cis-olefin group's =C-H out-of-plane mode and the progression bands due to CH(2) rocking-CH(2) twisting modes are expected to appear. The structural evolutions during the LT -> MT phase transition of linoleic acid were investigated by analyzing the progression bands with the simple-coupled oscillator model to elucidate the features of acyl chain influenced with two cis-C=C bonds linked through one CH(2) group. Structure changes in the LT -> MT transition of linoleic acid were compared with those in the gamma -> alpha transition of oleic acid. It has been found that the former is rather localized around the cis-diene group, while the latter occurs in the larger portion between the cis-olefin group to the methyl end. It is also suggested that the conformational change in the cis-olefin group on the LT -> MT transition is on a lesser scale than that on the gamma -> alpha transition.