The phase transitions for a homologous series of semifluorinated n-alkanes, F(CF2)(10)(CH2) mH, with 2 <= m <= 19 (F10Hm), have been characterized using a polarizing microscope, DSC, X- ray diffraction, and dilatometry. Thermal analysis and optical textures indicate the presence of the smectic- smectic phase transition when the number of methylene units ranges from 6 to 12. The phase- transition temperature depends on the length ( m) of the hydrocarbon segment. The density decreases with increases in the carbon number of the hydrogen segment. The data for both the thermal properties and the density suggest that the smectic- smectic phase transition is significantly first- order, which is primarily caused by a change in the molecular packing for the molecular rearrangement, while a transition for the clearing point is related to disordering of the entire molecule. The volume jump shows that F10Hm have the same molecular packing in the high- temperature mesophase and that their magnitude is greater than that of the conventional liquid crystalline compounds having an aromatic- mesogenic core. The effects of the fluorinated segment for the phase transitions are also discussed herein.