In　situ　ATR-FTIR　spectroscopy　has　been　extended　to　the　study　of　CO　and　pyridine　adsorptions　at　crystalline　and　amorphous　Ni-P　alloy　film　electrodes,　with　an　emphasis　on　the　alloying　effect　of　P　on　their　adsorption　configurations　on　Ni　sites.　The　Ni-P　films　were　prepared　with　initial　seeding　of　a　catalytic　Pd　layer　on　Si,　followed　by　chemical　deposition.　Transition　from　bridge-bonded　CO　(COB)　dominant　to　linearly　bonded　CO　(COL)　dominant　adsorption　was　found　with　increasing　P　content,　together　with　a　blue-shift　in　the　COL　vibrational　frequency　and　an　attenuation　of　the　Stark　tuning　rate　of　COL.　As　for　Py　on　Ni-P　electrodes,　essentially　the　N-end-on　adsorption　was　revealed,　in　contrast　to　the　edge-tilted　adsorption　on　Ni　electrode.　Modification　in　the　adsorption　configurations　as　compared　to　that　on　Ni　electrode　is　ascribed　mainly　to　the　site-blocking　effect　with　alloying　P,　rather　than　to　partial　electron　transfer　between　Ni　and　P.　©　2008　Elsevier　Ltd.　All　rights　reserved.