The first structurally authenticated example of coordinated polymer featuring homometallic pillared-trilayer structure, [Co-3(ina)(2)(PiCo)(2)(H2O)(2)](n) (1), was built from mixed pyridyl-type monocarboxylates, isonicotinate (ina) and 3-hydroxypicolinate (pico), containing Kagome-type [Co-3(Pico)(2)(H2O)(2)](n)(2n+) trilayers. The magnetic phase diagram of 1 shows a metamagnetic transition below 3.2 K, arising from the competing interactions between the antiferromagnetic intralayer couplings in different amplitudes with obviously noncompensated moments versus weak AF interlayer coupling.