The authors describe a microfluidic chip-based aptasensor platform combined with magnetic tripartite DNA structure-functionalized nanocomposites to achieve simultaneous determination of kanamycin (KANA), aflatoxin M1 (AFM1), and 17β-estradiol (E2) in milk. The two-duplex tripartite DNA nanostructure was first assembled on the surface of magnetic beads. When the aptamer on the probes recognized the specific target, the aptamer-target would be released into the supernatant. The pre-primer@circular DNA template structure initiates rolling circle amplification (RCA) by phi29 polymerase. After magnetic separation, the magnetic nanocomposites were added into a solution containing three different lengths of complementary strands to the RCA products. The number of complementary strands significantly decrease, and this can be quantitated by the microfluidic chip. Further, the employment of magnetic nanocomposites and microfluidic chip not only resolve the complex matrix interference, but also dramatically enhances the determination selectivity and sensitivity. This aptasensor allows for determination of KANA, AFM1, and E2 with limits of detection as low as 0.32 pg mL-1, 0.95 pg mL-1, and 6.8 pg mL-1, respectively. This novel method exhibits the advantages of excellent stability and fast response time (< 3 min on microfluidic chip platform) for simultaneous determination of KANA, AFM1, and E2 in milk samples and ensures food safety. Graphical abstract.