This paper represents the results of an experimental work on some properties of high-strength concrete containing different levels of silica fume. Silica fume is an ultrafine powder collected as a by-product of the silicon and ferrosilicon alloy production. A certain percentage of silica fume as a cement replacement, can improve some properties of high-strength concrete such as compressive strength, flexural strength durability etc. The main objective of this study was to determine the optimum percentage of silica fume to replace cement in order to improve the properties of hardened high-strength concrete. To fulfill the objective, some properties of concrete containing silica fume were evaluated after 7, 28 and 60 days of curing. Furthermore, comparison between regular concrete and silica fume concrete containing different levels of silica fume content (5%, 10% and 15%) was conducted. The water/binder ratio was kept constant at 0.3 throughout the mixing process. The results of this research work indicate that compressive strength and flexural strength exhibited the highest improvement with 10% and 15% silica fume replacement respectively. This paper can be a useful source of information for other researchers to understand the benefits and adverse effects of silica fume and have an overview of its optimum percentage when dealing with concrete.