An electrochemical DNA biosensor based on hexaammineruthenium（Ⅲ） chloride （［Ru（NH3）6］3+） as a hybrid indicator was fabricated for the detection of PML/RARα fusion gene in acute promyelocytic leukemia（APL） by chronocoulometry（CC）.The DNA probes were immobilized onto the surface of electrode via Au-S covalent bond，followed by the hybridization with target DNA complementary sequences.CC method was employed to monitor the hybridization events and contrast the charge variations before and after hybridization to quantitate the target DNA complementary sequences.Owing to the different amounts of ［Ru（NH3）6］3+ caused by electrostatic combination with DNA sequences before and after hybridization，the charge difference was formed.The increase of the different charge of ［Ru（NH3）6］3+ was observed upon the hybridization of the probe with target DNA，and the charge difference of ［Ru（NH3）6］3+ was enhanced with the increase of target DNA sequence concentration.Under the optimal conditions，experimental results indicated that the biosensor showed a good specificity to distinguish the complementary sequence from different mismatch sequences and could be used to detect PML/RARα fusion gene quantitatively.The relationship between the charge difference and logarithmic （lgc） of target sequence concentrations was linear in the concentration range of 1.0×10-12-1.0×10-8 mol·L-1，and the detection limit was 4.0×10-13 mol·L-1.Therefore，as an electrochemical DNA indicator of the DNA sensor，the［Ru（NH3）6］3+can be used to detect the complementary sequence of PML/ RARα fusion gene qualitatively and quantitatively.