The present study was conducted to evaluate the effect of polyculture shrimp, Litopenaeus vannamei with keeled mullet, liza carinata at different densitiescompared to the monoculture system on Physico- Chemical water quality. In a complete randomized design, 15 glass aquaria (80×30×40 cm - 96 L) randomly distributed into in 5 treatments group (in triplicates). Each aquaria was stocked with 12 aquatic animals. In first experimental group was stocked with L. carinata only as monoculture (T₁; Fish 100%). Similarly, second experimental group was stocked with
L. vannamei only as monoculture (T₂; Shrimp 100%). Experimental treatments of T3-T5 groups were stocked with both L. carinata and L. vannamei in polyculture at densities of (fish 25%: shrimp 75%), (fish 50%: shrimp 50%) and (fish 75%, shrimp 25%), respectively.Over the 12-weeks period, all water quality parameters were observed within the acceptable range for both L. carinata and
L. vannamei either monoculture orpolyculture systems. The results showed that water salinity was ranged between 30.15 to 32.30ppt, water temperature from 25.32 to 30.90°C, dissolved oxygen(6.17 to 7.09 mgL^-1) and pH (7.07 to 7.83)without any statistical differences (P ≥ 0.05).The concentration of phosphorous (PO₄) ranged from 00.05±0.02- 0.009±0.002mg/l. The highestPO₄ values was recorded for (T1) followed (T5). The highest TAN values was recorded for (T1) followed (T5), while the lowest values were recorded in either T3 or T2. The same trend was observed for NO₃. The concentration of NO₂ ranges from 0.001 to 0.09 mg/L. The results of present study suggested that a clear effect of mixed culture of L. carinata with L. vannamei in polyculture system to purify the water pond through food residues or undigested food and improve physico-chemical water quality.