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Chronic kidney disease (CKD) is a known risk factor for hypercalcemia in cats. Phosphate-restricted diets have also been implicated in causing hypercalcemia, in part because phosphate restriction increases the Ca:P ratio. The primary objective of this study was to evaluate the impact of two different therapeutic renal foods on ionized (iCa) and total (tCa) calcium concentrations in cats with early-stage CKD. Twenty colony-housed cats with stage 1 or 2 CKD were enrolled, and 18 cats completed the study. Cats were randomly assigned to receive one of two diets formulated for renal disease for 140 days: a moderately phosphate restricted food (M-PR; n = 10 cats; 1.8 g/Mcal calcium; 1.5 g/Mcal phosphorus; Ca:P ratio, 1.2:1) or a more highly phosphate restricted food (H-PR; n = 8 cats; 2.3 g/Mcal calcium; 1.1 g/Mcal phosphorus; Ca:P ratio, 2.0:1). Blood and urine samples were collected on Days 0, 28, 84, and 140. Data were analyzed using a linear mixed model with fixed effects of diet, day, and diet by day interaction. At baseline, all cats had iCa within the normal reference interval (1.10─1.30 mmol/L). On d28 and thereafter, cats fed H-PR food had higher iCa compared with cats fed M-PR food (day 140 means: 1.42 mmol/L vs. 1.24 mmol/L, respectively; p < 0.001). Results were similar for tCa (day 140 means: 11.49 mg/dL vs. 9.51 mg/dL, respectively; p < 0.001; normal reference interval 8.80-10.00 mg/dL). This corresponded to higher fractional excretion of calcium in urine in cats fed H-PR food (Day 140 means 1.18% vs. 0.19%; p < 0.001), and increased calcium oxalate (CaOx) stone formation risk metrics (Day 140 means for CaOx RSS 4.54 vs. 3.13; Day 140 means for CaOx CORI risk index 563 vs. 30/L, respectively; all p < 0.020). Cats fed H-PR food also had higher FGF-23 concentrations compared with cats fed M-PR food (Day 140 means: 2329 vs. 204 pg/mL, respectively; p = 0.003; normal reference interval ≤ 299 pg/mL), and lower calcitriol concentrations (Day 140 means: 94 vs. 186 pmol/L, respectively; p = 0.021; normal reference interval 90-342 pmol/L). PTH concentrations in cats consuming H-PR food were significantly decreased from their baseline means and from cats consuming M-PR food at all timepoints (Day 140 means: < 0.05 vs. 3.1 pmol/L, respectively; p < 0.050; normal reference interval 0.7-3.4 pmol/L). Therapeutic renal diets impact calcium status in cats with early-stage CKD, but the effect is formulation dependent. Cats fed a M-PR food maintained normal iCa and tCa, which suggests this food is a safe and well-accepted option for cats with early-stage renal disease.