A segmented/modular cooling tower fan cylinder having basic segments, a motor segment and an access segment, assembled to form an hourglass shaped cooling tower fan cylinder to protect fan blades, reduce sound and vibration, and enhance performance. The segments are preferably molded fiberglass composite structures having integrally molded vertical and horizontal ribs and a horizontal rib stiffener which connects horizontal ribs of adjacent segments. A top ring stiffener is provided at the junction of each two adjacent segments in the top ring flange. Lifter bars may be provided inside a central vertical rib of the segment to secure cables or straps to hoist an assembled fan cylinder into its final location or to secure a safety harness for workers servicing equipment in the interior space defined by the fan cylinder.