Herein, we presented a "signal-on" switch electrochemiluminescence (ECL) biosensor based on molecular recognition and nanocomposite to track circulating tumor cells (CTCs) in real time. CTCs are well-known biomarkers for metastasis. To construct the ECL biosensor for CTC detection, the surface of a glassy carbon electrode (GCE) was first modified with the composite of Ru(bpy)(3)(2+)/beta-cyclodextrin-Au nanoparticles(beta-CD-AuNPs)/graphene, followed by immobilizing ferrocene-labeled aptamers (TLS1c and TLS11a in 1:1 ratio) as the probes (Fc-aptamers/Ru(bpy)(3)(2+)/beta-cyclodextrin-Au nanoparticles(beta-CD-AuNPs)/graphene). In presence of the CTCs, the quencher (Fc) left the electrode after connecting with aptamers, thus enhancing ECL signal, i.e., recovering the "signal-on". This newly developed ECL biosensor demonstrated supersensitive, selective, rapid detection of the CTCs with a detection limit of 40 cells mL(-1). In addition, the biosensor exhibited excellent reusability with at least 6 cycles of recovering the original signal. Therefore, this aptamer based "signal-on" switch electrochemiluminescence (ECL) biosensor may help in assessing the prognosis of patients with cancer metastasis.