An adjustable rotating shaft guard (1) includes a base, a first guard half (12), and a second guard half (14). A bottom of the first and second guard halves are retained by the base such that they contact each other to fully cover a rotating shaft or coupler. A half sleeve (18) preferably extends outward from at least one end of the first and second guard halves (12,14). Preferably, the top of each guard half is fastened to each other. The first and second guard halves (12,14) are preferably fabricated from a high impact plastic. The bottom area of the first and second guard halves (12,14) preferably have a plurality of cutting lines (36) which provide a reference for sawing to a specific height. The half sleeves (18,20) also have a plurality of cutting lines (40) which provide a reference for sawing to a specific length. In a second embodiment, an adjustable rotating shaft guard (2) includes a first sleeve guard half (42), a second sleeve guard half (44) and two sets of two end cap halves (46,48). Each pair of end cap halves (46,48) are attached to each end of the first and second sleeve guard halves (42,44). One or both ends of the first and second sleeve halves (42,44) may be supported by an adjustable leg set. One or both ends of the first and second sleeve guard halves (42,44) may be supported by a mounting plate.