River Ngong, one of the major rivers in the Nairobi river basin receives enormous amounts of solid and liquid waste from industrial and domestic discharges. This exposes the river to high pollution. An environmental concern arises especially on its unknown levels of hazardous persistent organic pollutants in particular the polycyclic aromatic hydrocarbons (PAH). Notably, its untreated water from some sections along its course is used for domestic purposes hence poses human health risks that may be attributed to long term exposure and accumulation of PAH. United States Environmental Protection Agency (US EPA) not only identifies sixteen priority PAHs that are carcinogenic and mutagenic but alongside other world bodies including WHO, have recommendations for their allowable threshold in water. Previous studies on this river have focused on pollutants such as heavy metals, microbiological contaminants, polychlorinated biphenyls and many other persistent organic pollutants. However there is no literature on the levels of PAHs in this river hence the need for this study. Data from Nairobi cancer registry indicate that cancer cases are on the rise. This can be attributed to a number of factors ranging from nutrition, physical life style to fears of exposure to possible sources of carcinogenic compounds such as PAHs. The aim of the study was to determine levels of sixteen (16) US EPA priority PAHs in water in the Ngong River and compare the levels to the WHO/US EPA standard maximum level. Physico-chemical parameters and levels of the sixteen US EPA priority PAHs in water sampled from sections along the Ngong River are reported, the latter using GC-MS. In some sampling points, turbidity, dissolved oxygen and electrical conductivity were found to divert from the recommended thresholds and overall, the total concentrations of the PAHs ranged between 2.69 ng/L and 14.22 ng/L. Although PAH levels were found to be within acceptable levels, precaution need to be adhered to in the use of untreated water from River Ngong in fear of body accumulation of PAHs and their dangers.