High precision measurements of magnetoresistance =f(T,H) and magnetization M(T,H) have been carried out on single crystals of rare earth dodecaboride TmB12 at temperatures 1.8–30 K in magnetic fields up to 80 kOe. The high accuracy measurements and precise temperature stabilization allowed us to perform numerical differentiation and analyze quantitatively a behavior of derivative d()/dH=f(T,H) and magnetic susceptibility (T,H)=dM/dH in paramagnetic and magnetically ordered phases of thulium dodecaboride. It was shown that negative magnetoresistance anomalies observed in present study in paramagnetic state of TmB12 can be consistently interpreted in frameworks of a simple relation between resistivity and magnetization - /M2 proposed by K. Yosida (Phys. Rev., 107, 396 (1957)). A local magnetic susceptibility loc(T,H)=(1/H(d(/)/dH))1/2 was deduced directly from the magnetoresistance measurements and compared with bulk susceptibility (T,H)=dM/dH results of the present study. Moreover, the susceptibility dependences loc(T,H) and (T,H) have been applied to analyze in detail the H-T magnetic phase diagram of TmB12.