Atomic force microscopy (AFM) on Langmuir-Blodgett (LB) films of alkyl-tetracyanoquinodimethanes (alkyl-TCNQs) have been carried out. The two-dimensional periodic molecular arrangements are observed on the surface of each LB films. The observed periodic structure due to the two-dimensional molecular arrangements in the LB films of C-12- (a(0) = 0.83 +/- 0.02 nm, b(0) = 0.47 +/- 0.01 nm, and gamma = 95 +/- 2 degrees) and C(18)TCNQ (a(0) = 0.83 +/- 0.02 nm, b(0) = 0.48 +/- 0.01 nm, and gamma = 94 +/- 2 degrees) are almost identical with each other, while that of the C(15)TCNQ (a(0) = 0.78 +/- 0.03 nm, b(0) = 0.47 +/- 0.01 nm, and gamma = 101 +/- 2 degrees) is different from those films. Since the alkyl-TCNQ LB films consists of bimolecular layers, the observed images are due to the two-dimensional arrangements of the TCNQ chromophores. Thus, the difference in the way of subcell packing of the alkyl chains must affect the packing of the TCNQ chromophores, and the difference of the molecular arrangements seems to depend on an even or odd number of the length of the alkyl chain. These results agree with the result of infrared spectroscopy : the alkyl chains in the LB films of C-12- and C(18)TCNQ crystallize with orthorhombic subcell packing, while those of C(15)TCNQ are in the hexagonal or pseudohexagonal subcell packing.