Transmission electron microscopy (TEM) and electron energy-loss spectroscopy (EELS) have been used to characterize the structure and microstructure of the low La-doped layered manganite La (x) Sr4-x Mn3O10 (x <= 0.15). The structure of the perfect phase has been identified as an n = 3 layered structure of the hexagonal series by electron diffraction (ED), high-resolution electron microscopy (HRTEM) together with numerical image simulations. The presence of local superstructure modulation associated with La ordering in the compounds was revealed by electron diffraction and high-resolution electron microscopy. Electron diffraction data indicate that this superstructure modulation is two-dimensional, and the modulation plane lies in the ac plane. The two primary modulation vectors are q(1) = (1/4)a* and q(2) =(1/2)c*. In addition, another type of modulated structure associated with periodic lattice distortion was occasionally visible in the La0.15Sr3.85Mn3O10 phase. Energy-loss spectroscopy data indicate that the periodic lattice distortion is led by ordered oxygen deficiency.