Abstract: The size, distribution characteristics, precipitation law, and composition of precipitate particles in ferrite matrix Ti-Mo micro-alloy steel with two different titanium contents were studied by metallographic microscopy, transmission electron microscopy and energy dispersive spectroscopy. Most of the precipitate particles are ultra fine carbides of less than 10 nm in size, and the particle sizes are a normal distribution. With the increase of titanium content from 0. 072% to 0. 092%, the average particle size increases and the distribution peak gradually moves to the particle size increasing direction. The Ti-Mo micro-alloy steel has an inter-phase precipitation style like ledge structures. The ledge spacing in the interior grain is different from that near the grain boundaries, and it is affected by cooling rate. Energy spectrum analysis shows that the Mo content is different in different sizes of particles. The composition of the bigger particles (about 50 nm) has no molybdenum, but the smaller particles (less than 20 nm) are compound of Ti and Mo. The Mo content increases with the particle size decreasing.