Abstract: The precipitation behavior of FeTiP phase in P-added high strength IF steel, as well as its influence on the hardness were analyzed. The precipitation hardening effect in P-added IF steel was found. The experiment demonstraes that the hardening effect is more obvious during the aging at 550℃. The key reason of the hardening is the fine precipitation of FeTiP phase, which precipitates not only on the grain boundaries but also inside the grains.The atom ratio of Fe:Ti:P of FeTiP phase is not the exact ratio of 1:1:1 during the aging at 750℃. It is believed that the hardening effect induced by non-carbontrides e. g. FeTip in high purity and ultra-low carbon micro-alloyed steel should be investigated further.