A study of 47 adults older than 60 years examined the effects of frailty and walking speed on gait variability using inertial sensors at preferred, fast, and slow speeds. Endpoint variability was assessed by standard deviations of support time, lower limb coordination by continuous relative phase (CRP) analysis for inter- and intralimbs with coefficient of variability (CV). An interaction of frailty and speed was found on the total variability of support time (p=0.044, ηp²=0.116), knee-ankle CV during braking phase (p=0.020, ηp²=0.123) and propulsive phase (ηp²=0.170). Frail and pre-frail groups had greater variability in total support time during fast walking (p=0.036 and p=0.011), especially knee-ankle and hip-hip (p<0.018 and p<0.001). The greatest variability of support time was during fast walking (frail: p=0.015; pre-frail: p<0.001) and knee-ankle CV at preferred speed (p=0.016 and p=0.017). Frailty reduced CV hip-hip (p<0.001, ηp²=0.933), ankle-ankle (p=0.014, ηp²=0.175) in the braking phase and knee-knee in the propulsive phase (p<0.001, ηp²=0.511). Speed affected CV differently, e.g. the largest CV at the preferred speed for the hip-knee in the propulsion phase (p=0.011). The study has a cross-sectional design with a limited sample, recommending longitudinal validation.