Osmium hydrido vinylidene 1 shows diverse cyclization reactivity with activated terminal alkynes. Treatment of 1 with HCCCOR′ (R′=OEt and Me) gave osmafurans 3 a and 3 b via osmium alkenyl/vinylidenes 2 a and 2 b. In addition, 1 reacted with HCCCH(OH)CCH to yield osmabenzene 4, in which the alkynol acted as a C5 fragment to cyclize with 1. Mechanistic analysis indicates that these reactions and the previous formal [3+3] cycloadditions between 1 and HCCCH(OH)R (R=Ph, Et, and vinyl) or HCCCH(OEt)2 all go through similar osmabutadiene intermediates. Subsequently, the intermediates either took a “coordination and cyclization” process or a “carbon–carbon coupling” path to cyclization, depending on the coordination ability of substituents on the terminal alkenyl carbon atom.