Abstract: Mecbanical Properties and microstructure of low carbon manganese clean steels microalloyed with Nb, Ti, B were studied. High levels of yield strength (>800 MPa) have been attained in the tempered steel containing 0.06%C,2.3%Mn, 0.21%Al and small amount of Nb, Ti, V, B. The elongation elongation of this steel is more than 14% and V-notch toughness is 134~174.5 J/cm² and 103~110J/cm² at room temperature and -40 respectively. Very for bainitic structure (with lath width in micrometer or less) was observed in the steel. Effects of deformation as well as Al additive on the austenite-bainite transformation and mechanical properties have been investigated.