Knowledge on saliva sodium (Na), potassium (K), and phosphorus (P) concentrations are important in modeling electrolyte, water, and P partitioning in dairy cows. Saliva mineral concentrations in ruminants are strongly associated with saliva secretion rates, which can be affected by diet composition. The objective of this study was to examine saliva Na, K, and P concentrations in lactating cows fed 2 levels of forage and CP contents. Saliva samples were collected from 12 lactating Holstein cows randomly assigned to a 2 × 2 factorial arrangement of 2 forage (alfalfa hay) levels [38 (LF) vs. 53% (HF)] and 2 CP levels [15.2 (LP) vs. 18.5% (HP)] over 3 periods. Saliva samples were acidified (pH = 5–6) and diluted by a factor of 50 using deionized water (pH = 4.0). The filtered samples were then analyzed for Na, K, P, and calcium (Ca) concentrations by inductively coupled plasma atomic emission spectroscopy. Treatment effects on saliva mineral concentrations were analyzed with mixed-effect models including random cow effect. Mean dietary concentrations and total intake (via feed and water) of Na, K, and P were 0.36 ± 0.01, 1.04 ± 0.10, and 0.40 ± 0.01% of DM and 81 ± 10, 236 ± 40, and 93 ± 9 g/cow/d, respectively. Only total K intake was negatively affected by dietary fiber content (P < 0.01). Saliva concentrations of Na and K were on average 70.3 ± 6.7 and 21.9 ± 1.3 mmol/L and were negatively correlated (r = –0.40, P < 0.01). A unit increase in average daily temperature (T, °C) increased and decreased saliva K (P = 0.08) and Na (P = 0.05) concentrations by 0.9 ± 0.5 and 4.9 ± 2.4 mmol/L, respectively. Saliva K concentration decreased by 0.010 ± 0.005 mmol/L (P = 0.07) for unit increase in BW. Saliva P concentration was on average 1.9 ± 0.4 mmol/L, and increased and decreased by 0.004 ± 0.002 (P = 0.10) and 0.61 ± 0.18 mmol/L (P < 0.01) for unit increase in BW and T. Saliva P concentration was negatively related to saliva Ca concentration (r = –0.37, P < 0.01). Dietary fiber or CP contents did not have significant effect on any of the saliva mineral concentrations. Information on BW, T, and relationship with other minerals are important in determining Na, K, and P partitioning in lactating dairy cows.