Ultra-high-performance concrete (UHPC) is a new and innovative concrete material associated with very high strength, low permeability to aggressive environment and self-compact ability. These characteristics enable innovative engineering solutions to be applied in practice which would have previously been thought to be impossible to manufacture. Many previous studies suggest relatively high dosage rates of micro silica (MS) (25% by weight of binder (wtob)). This paper focuses on optimizing and studying how the MS addition to UHPC affects the compressive strength and overall rheological properties of UHPC. The study was performed by doing compressive strength tests as well as concrete slump flow tests to evaluate the rheology and slump flow over a period of time to evaluate how well the mix retains its initial rheological properties. It was found that the compressive strength was enhanced the most by 3.75% by wtob of MS substitution. The best rheology for self-compact ability was obtained by substituting MS between 5% and 7.5% by wtob. It was also found that increase an in MS dosage rate will reduce the open life of fresh concrete.