The aim of this study was to quantify the effect that barbell load has on the jump height and force-time characteristics of the countermovement jump (CMJ). Fifteen strength-trained men (mean ± SD: age 23 ± 2 years, mass 84.9 ± 8.1 kg, height 1.80 ± 0.05 m) performed three CMJ with no additional load, and with barbell loads of 25%, 50%, 75%, and 100% of body mass on two force plates recording at 1000 Hz. Propulsion and landing force-time characteristics were obtained from force-time data and compared using analysis of variance and effect sizes. Jump height decreased significantly as load increased (26 to 71%, d = 1.80 to 6.87). During propulsion, impulse increased with load up to 75% of body mass (6 to 9%, d = 0.71 to 1.08), mean net force decreased (10 to 43%, d = 0.50 to 2.45) and time increased (13 to 50%, d = 0.70 to 2.57). During landing, impulse increased as load increased up to 75% of body mass (5 to 12%, d = 0.54 to 1.01), mean net force decreased (13 to 38%, d = 0.41 to 1.24), and time increased (20 to 47%, d = 0.65 to 1.47). Adding barbell load to CMJ significantly decreases CMJ height. Furthermore, CMJ with additional barbell load increases landing phase impulse. However, while mean net force decreases as barbell load increases, landing time increases so that jumpers are exposed to mechanical load for longer. Practitioners should exercise caution when implementing loaded CMJ to assess their athletes.