Lightning strokes to transmission lines have been estimated using the electro-geometric model proposed by Armstrong and Whitehead. The observed results of the lightning to large-scale transmission lines are reported here to validate the calculated results, in which ultra high voltage (UHV) designed transmission lines and 500 kV transmission lines were selected as the subjects of the observation. Lightning observations were carried out for direct strokes to phase conductor caused by shielding failures, as well as strokes to ground wires that have rarely been previously reported. The observed results showed that total number of direct lightning strokes to phase conductor were nearly identical to the calculated results based on the conventional method, while observed strokes to upper phase were larger and strokes to lower phase were smaller than those derived from calculations. It was also revealed that lightning strokes to ground wires of UHV designed transmission lines and 500 kV transmission lines were 5.1 times and 2.7 times larger, respectively, than calculated results based on the conventional method.