Ferromagnetic　3d　transition　metal　nanowires　based　on　the　assembly　of　shape　anisotropy　seem　apt　candidates　to　replace　materials　based　on　rare-earth　elements　in　current　permanent　magnets.　Recently,　great　efforts　have　been　devoted　into　enhancing　the　coercivity　of　Co　nanowires,　through　accurate　control　of　shape　and　morphology.　Nevertheless,　stacking　faults　can　be　formed　relatively　easily　in　close-packed　metals　like　Co,　and　its　effect　on　the　magnetic　properties　was　usually　obscured　by　the　geometrical　effect　and　being　ignored.　In　this　work,　the　Co　nanowires　with　different　aspect　ratios　were　synthesized　by　solvothermal　chemistry　processes.　The　effect　of　aspect　ratio　on　the　magnetic　properties　of　Co　nanowires　was　investigated,　and　a　high　magnetic　property　with　a　coercivity　of　9　kOe　was　obtained　in　the　Co　nanowires　with　an　aspect　ratio　of　10.　The　stacking　faults　were　observed　in　the　Co　nanowires　with　an　aspect　ratio　beyond　10,　which　may　be　a　contributing　factor　to　the　lower　coercivity　than　expected.　The　micromagnetic　simulation　was　employed　to　reveal　the　effect　of　stacking　faults　on　the　magnetization　reversal　mechanism,　based　on　which　the　coercivity　degradation　mechanism　was　discussed.　This　work　is　instructive　for　developing　high-performance　magnetic　nanowires.