We propose muSR study on magnetic properties of an organic charge transfer complex on a 2D triangular lattice, (C2H5)2(CH3)2Sb[Pd(dmit)2]2. This system has been known to exhibit charge separation forming spin-singlet below 70 K from the result of an X-ray analysis for the last decade. Our previous muSR result also revealed formation of the spin-singlet state. However, the transition temperature observed in the muSR was higher than that obtained from the X-ray analysis. Very recently, a new incommensurate phase has been found at the temperatures from 80 to 105 K, where competition between charge, spin and structural order exists, in a high-resolution X-ray diffraction measurement. The transition temperature of 105 K consists with the previous muSR result, but we have only poor data points under ZF. We will investigate magnetic state and dynamics in the newly discovered phase in detail.