Abstract: Background and Objective: Seasonal variations of physicochemical properties exert a very serious influence on the occurrence and abundance of both aquatic flora and fauna. Impact of physicochemical properties on benthic macro-invertebrates of Erelu reservoir was investigated. Materials and Methods: Water and benthic samples were collected monthly from June, 2013 to May, 2015 from 7 stations. Temperature and transparency were determined in situ with mercury in glass thermometer and secchi disc. Other water quality parameters were analyzed using standard methods, while benthic macro-invertebrates were collected using Van-veen grab of 66.6 cm2. Benthos identification was done with standard identification guide. Species diversity and abundance were examined using Margalef, Shannon wiener and other indices. Data collected were analyzed using descriptive statistics and Pearson’s correlation coefficient. Results: Turbidity, NO3–, DO were higher in values in rainy season while transparency, temperature, BOD and EC values were high in dry season. The EC, Temp. TDS and transparency had inverse correlation with all orders of benthic macro-invertebrates. Turbidity and phosphate was significantly (p<0.05) related with Hygrophila (0.713) and Capitellida (0.942). The NO3– and TA had significant inverse correlation with (Unionidea). Conclusion: Physical and chemical properties of Erelu reservoir had significant seasonal variations and benthic macro-invertebrates abundance are independent of the physicochemical parameters excepts turbidity, phosphate and nitrate that influenced the abundance of some orders of benthic macro-invertebrates.