This study aimed at determining the effect of Kaduna Refinery on water quality of River Romi, Kaduna, Nigeria. The study was conducted for a period of six months, February to July, 2015. Water samples and plankton samples were collected from five different selected sites along River Romi.Some physicochemical parameterssuch as temperature, pH, TDS and EC were measured with HANNA instruments. Other physicochemical parameters measured include: DO, BOD, COD, PO4, NO3, SO4, total phosphorous, total nitrogen, hardness, alkalinity, oil and grease based on American Public Health Association (APHA) method; concentrations of each selected metal ion were read against the standards on a Buck Scientific model 200A Atomic Absorption Spectrophotometer (AAS).Analysis of Variance (ANOVA) and correlation analysis were used to analyse the data generated. The study revealed the following: temperature (27.78Â�C), pH (7.71), electrical conductivity (123.29μS/cm), TDS (61.99mg/L), DO (4.05mg/L), BOD (2.32mg/L), COD (419.07mg/L), PO4 (0.13mg/L), NO3 (2.31mg/L), SO4 (6.94mg/L), total phosphorous (1.85mg/L), total nitrogen (20.98mg/L), hardness (186.87mg/L), alkalinity (54.80mg/L) and oil and grease (0.15mg/L). The concentration of heavy metals increased in this order: Nickel (0.15mg/L) < Lead (0.19mg/L) < Zinc (0.24mg/L) < Manganese (0.44mg/L) < Chromium (0.52mg/L). Phytoplankton species composition was higher than the zooplankton species.The highest number of species encountered was inStigonema sp. (752) and the lowest was observed in Closterium sp. and Pleurogaster sp. with one each, while, zooplankton had highest and lowest number in Paramaecium sp. (49) and Heliodiaptomus sp. (6). Some surface water parameters had influence on the distribution of plankton species. These findings suggested that most of the physicochemical parameters were above the acceptable limit of the portable water for domestic use which may be due to industrial effluent, house waste discharges and agricultural activities that are taking place in the vicinity of River Romi.