Structural features of the charge/orbital ordering (CO∕OO) in single-layered manganites Pr1−xCa1+xMnO4 (0.3⩽x⩽0.65) have been investigated systematically by transmission electron microscopy. Analyses of electron-diffraction patterns as well as dark-field images have revealed that the CO∕OO shows a striking asymmetric behavior as the hole doping x deviates from x=0.5. The modulation wave number linearly decreases with increasing x in the over-hole-doped (x>0.5) crystals, while much less dependent on x in the under-hole-doped (x<0.5) crystals. A temperature-induced incommensurate-commensurate crossover is observed in 0.35<x<0.5 and x=0.65. The correlation length of CO∕OO in x=0.3 was proven to become shorter than that in 0.35⩽x⩽0.65