During mitosis, motor proteins and microtubule-associated protein organize the spindle apparatus by cross-linking and sliding microtubules. Kinesin-5 plays a vital role in spindle formation and maintenance, potentially inducing twist in the spindle fibers. The off-axis power stroke of kinesin-5 could generate this twist, but its implications in microtubule organization remain unclear. Here, we investigate 3D microtubule-microtubule sliding mediated by the human kinesin-5, KIF11, and found that the motor caused right-handed helical motion of anti-parallel microtubules around each other. The sidestepping ratio increased with reduced ATP concentration, indicating that forward and sideways stepping of the motor are not strictly coupled. Further, the microtubule-microtubule distance (motor extension) during sliding decreased with increasing sliding velocity. Intriguingly, parallel microtubules cross-linked by KIF11 orbited without forward motion, with nearly full motor extension. Altering the length of the neck linker increased the forward velocity and pitch of microtubules in anti-parallel overlaps. Taken together, we suggest that helical motion and orbiting of microtubules, driven by KIF11, contributes to flexible and context-dependent filament organization, as well as torque regulation within the mitotic spindle. Synopsis Kinesin motors are involved in organizing the mitotic spindle by cross-linking and sliding microtubules. This work shows that the sideways stepping of human kinesin-5, KIF11, causes helical motion of anti-parallel microtubules and orbiting motion of parallel microtubules. KIF11 drives a right-handed helical motion of short microtubules around long, suspended microtubules in anti-parallel overlaps. The microtubule-microtubule distance (i.e., motor extension) decreases with increasing sliding velocity. KIF11 drives an orbiting motion of parallel microtubules at nearly full motor extension. Altering the length of the KIF11 neck linker increases forward velocity and pitch of microtubules in anti-parallel overlaps. Sideways stepping of human KIF11 causes helical and orbiting motions of microtubules that may contribute to flexible filament formation and mitotic spindle torque regulation.