The main aim of this paper was to evaluate the effects of short- term (6 days) phosphate loading, as well as prolonged (21 days) intake of sodium phosphate on aerobic capacity in off-road cyclists. Nineteen well-trained cyclists were randomly divided into a supplemental (S) and control group (C). Group S was supplemented for 6 days with tri-sodium phosphate, in a dose of 50 mg·kg^-1 of FFM/d, while a placebo was provided for the C group. Additionally, group S was further subjected to a 3-week supplementation of 25 mg·kg^-1 FFM/d, while group C received 2g of glucose. The results indicate a significant (p < 0.05) increase in VO₂max, VE_max, and O₂/HR, due to sodium phosphate intake over 6 days. Also a significant (p < 0.05) decrease in HR_rest and HR_max occurred. The supplementation procedure caused a significant increase (p < 0.05) in P_max and a shift of VAT towards higher loads. There were no significant changes in the concentration of 2,3-DPG, acid-base balance and lactate concentration, due to phosphate salt intake.