This  study  was  carried  out  to  evaluate  the  water  quality  of  Oyan reservoir  for  irrigation purpose.  Water samples were collected from thirty two (32) different locations along the reservoir i.e. upstream, midstream and downstream for the determination of sixteen (16) physicochemical parameters following standard methods, based on these analyses, some irrigation parameters like magnesium content(MC), sodium absorption ratio(SAR), residual sodium carbonate (RSC), permeability index (PI), Kelly's index(KI), and sodium percent(SP) were calculated following standard equations.  The results ranged from 7.1 to 8.5pH, 135.8 to 148.7µmhocm^-1, 86.91 to 95.17mgL^-1 TDS, and 26.6 to 40.2NTU turbidity, 28.0 to 28.8⁰C temperature to 65 mgL^-1 total hardness, 11.7 to 16.8  mgL^-1 Cl, 0.0 to 1.433 meqL^-1   HCO₃, 0 to 1.667meqL^-1 CO₃^-2, 0.1976 to 1.198meqL^-1 Ca²⁺, 0.196 to 0.783 meqL^-1 Mg²⁺, 0.058 to 0.216meqL^-1 Na⁺, 0.064 to 0.082meqL^-1 K⁺, 3.1 to 8.5mgL^-1 PO₄^-3, 0.2 to 1.08mgL^-1 NO₃^-, 0.01 to 0.08mgL^-1 SO₄^2-, 21.89 to 74.64meqL^-1 MC, -0.462 to 1.414meqL^-1 RSC, 0.079 to 0.3168meqL^-1 SAR, 12.12 to 147.92meqL^-1 PI, 11.02 to 24.44meqL^-1 SP and 0.054 to 0.238meqL^-1 KI.  Based on the guideline by FAO (Food and Agricultural Organization) interpretation of water quality for irrigation, the results of analyses and assessment of water quality from Oyan reservoir revealed that they are suitable for irrigation purposes.