Acidithiobacillus caldus is an acidophilic, chemoautotrophic bacterium, plays important role in bioleaching. Gene transformation into A. caldus is difficult and only the conjugation method was reported successful, which method was relatively sophisticated. In this research, electrotransformation of A. caldus species was achieved for the first time using A. caldus Y-3 and plasmid pJRD215. Transformants were confirmed by colony PCR specific to the str gene on pJRD215, and the recovery of the plasmid from the presumptive transformants. Optimizations were made and the transformation efficiency was increased from 0.8 to 3.6 x 104 transfomants/microng plasmid DNA. The developed electrotransformation method was convenient in introducing foreign genes into A. caldus.