Golf courses often present sloped surfaces that require players to adjust their swing mechanics. Understanding these adaptations is important for optimizing performance and maintaining consistency. This research studied how low-handicap golfers adjusted their body when performing golf swings on flat, uphill, and downhill slopes. Sixteen right-handed male university golfers (mean age 21.4 ± 2.4 years; body height 177.7 ± 4.7 cm; body mass 80.4 ± 11.0 kg; handicap 3.6 ± 1.6) performed swings using a 7-iron to swing on flat (0°), uphill (+10°), and downhill (−10°) slopes. The golfers’ movements were recorded using an optical motion analysis system. Kinematic data were analyzed using one-dimensional statistical parametric mapping (SPM 1D) with one-way repeated measures ANOVA. Significant differences (p < 0.05) were found in lower-limb joint angles and upper body inclination across slope conditions, while no significant differences were found in clubhead speed or pelvis and thorax rotation velocity. The findings show how golfers adjusted their posture to compensate for the slope while maintaining clubhead speed despite these postural changes. Initially, golfers addressed the ball by shortening the upper-side leg and aligning the upper body parallel to the slope. During the downswing, they gradually shifted their upper-body inclination toward a more upright posture relative to the ground, with lower-limb adaptations differing between the uphill and downhill conditions. These adjustments serve as strategies to sustain clubhead speed and optimize performance during uphill and downhill swings.