A series of oleic acid (OA) analogs containing terminal perfluoroalkyl groups (CF 3 , C 2 F 5 , n-C 3 F 7 , n-C 4 F 9 or n-C 8 F 17 ) was synthesized to clarify how the fluorinated chain length affects the stability and molecular packing of liquid-expanded OA monolayers at the air–water interface. Although the substitution of terminal CF 3 group for CH 3 in OA had no effect on monolayer stability, further fluorination led to a gradual increase in monolayer stability at 25̊C. Surface pressure–area isotherm revealed that partially fluorinated OA analogs form more expanded monolayers than OA at low surface pressures, and that the monolayer behavior of OA analogs with the even-carbon numbered fluorinated chain is almost the same as that of OA upon monolayer compression, whereas the behavior of OA analogs with the odd-carbon numbered fluorinated chain significantly differs from that of OA. These results indicate: (i) the terminal short part (at least C 2 residue) in OA predominantly determines the liquid-expanded monolayer stability; (ii) the molecular packing state of OA may be perturbed by the substitution of a short odd-carbon numbered fluorinated chain; (iii) hence, OA analogs with even-carbon numbered chain are considered to be preferable as hydrophobic building blocks for the synthesis of fluorinated phospholipids.