Stylet penetration behaviors of Bemisia tabaci biotype B on two transgenic cotton lines 'GK12' and 'GK19' expressing Bt toxic protein Cry1A (Bt cotton) and a non-Bt conventional cotton line 'Simian-3' (CK cotton) were recorded with the direct current electrical penetration graph (DC-EPG) technique. Our results suggested that EPG waveform patterns, types and characteristics non-probe (NP), pathway (C), potential drops (pd) and phloem phase (E(pd)) of Bemisia tabaci biotype B were very similar on the three cotton lines. There were no obvious differences of pathway variables among whiteflies on the three cotton lines. Some phloem variables related to E(pd)1 differed. Duration of 1st E(pd)1 and mean duration of E(pd)1 on both GK12 and GK19 were significantly shorter than that on CK cotton (P &lt; 0.05). Fewer whiteflies on GK have long E(pd)1. Other phloem variables including total duration of E(pd) summed, mean E(pd) duration and percentage of whiteflies reaching the phloem phase were similar among the three cotton lines.