The present study was conducted to evaluate the effect of salinity and Ca++ : Mg++ on the physiological and production parameters of Litopenaeus vannamei reared in inland saline ground water. A 60 days experiment was conducted at three different salinities as three treatment groups T1 (5 ppt), T2 (10 ppt) and T3 (15ppt) at different Ca: Mg ratio of 1:1, 1:2. 1:3 and 1:4 and L. vannamei juveniles weighing about 3.70 ± 0.02 g were stocked randomly in 100 L capacity plastic tanks fortified with 100% K+ to maintain the levels at par with the equivalent salinity sea water. There was 100% survival obtained in treatment groups T2 (10 ppt) and T3 (15 ppt) with a Ca: Mg (1:3). The better performance for various growth parameters like SGR, FCR, FER and PER were obtained at treatment groups T2 (10 ppt) and T3 (15 ppt) with a Ca: Mg (1:3). Growth of L. vannamei juveniles has been observed to be dependent on salinity and Ca++ / Mg++. A positive correlation has been observed between the level of Ca++ / Mg++ ratio in the medium and growth of the juveniles. Morphological changes like white muscle and muscle cramping were observed in all the treatment groups with 1:1, 1:2 and 1:4. A reduction in the growth was observed in all the treatment groups with Ca++ / Mg++ of 1:1. The crude protein content of the muscle was found to be increased with increase in salinity. A linear relationship between salinity and serum osmolality was also observed. No significant difference was observed among the treatment groups in osmoregulatory capacity due to interactive effect of Ca: Mg and salinity. Overall, the best production parameters were attained in the treatment group, T3 i.e., at 15 ppt with Ca: Mg ratio of 1:3, followed by T2 at 10 ppt with Ca: Mg ratio (1:3). Significant improvement in the performance of L. vannamei had been observed with the improvement in the Ca: Mg ratio from 1:1 to 1:3 at all the tested salinities. So it can be concluded that for better growth performance, survival and body composition of L. vannamei in inland saline water a salinity of 15 ppt with Ca: Mg ratio at 1:3 is optimum.