Carbon nanotubes (CNTs) were synthesized catalytically by both chemical vapor deposition (CVD) method in C2H2/H-2 atmosphere at 600 degreesC and arc-discharge (AD) method under helium atmosphere. The structure and morphology of CNTs was determined employing scanning electron microscopy (SEM) and FT-Raman spectroscopy. Hydrogen storage capacities were electrochemically measured for undoped and alkali metal (Li, Na and K) doped CVD, AD and laser ablation (LA) grown CNTs. The amounts of hydrogen stored were calculated from the measured discharge capacities. LA grown CNTs produced the highest hydrogen storage capacity of 1.6 wt%. The alkali metal-doped CNTs showed higher hydrogen storage capacities than un-doped CNTs. Although the hydrogen storage capacities of Li-doped CVD and AD grown CNTs were 6 times higher than that of un-doped CNTs, it is only 0.6 wt%. For Li-doped LA grown CNTs, the hydrogen storage capacity reached 2.4 wt%. The high hydrogen storage capacity of alkali metal-doped CNTs seems to be originated from increasing the hydrogen adsorption sites of CNTs due to introducing the doped metals in nanotube bundles and separating the tubes but not from their chemical effects.