lambda-(BETS)2GaCl4 is a non-magnetic anion-based organic superconductor SC attracting interest since its Fe analog becomes superconductor by applying 33 T. Both have similar Tc ~5 K. We measured TF and ZF-mSR down to 0.3K in the powder sample. The temperature dependence of the damping rate s(T) of the muon-spin precession related to the penetration depth was investigated in TF= 30 and 60 G. They indicate that SC is not stabilized even at 0.3 K or that there are nodes in the SC gap. We found a possible signature of time-reversal symmetry breaking (TRSB) since we detect slightly enhancement of relaxation rate below Tc in ZF-mSR. For extracting intrinsic & clear result, we are now planning to measure single crystals which can be aligned to make angular dependence measurement possible. We plan to align crystals in order to measure s(T) and TRSB and discuss SC gap symmetry by TF and ZF-mSR.