The　oil-tanning　mechanism　was　studied　in　detail　with　regard　to　the　tanning　effect　of　an　alkyl　sulfonyl　chloride　on　pickled　pigskins,　rabbit　skins　and　sheepskins.　Aldehyde　pre-tanned　rabbit　skins,　goat　skins　and　splits　of　pigskins　were　also　studied.　The　effect　on　shrinkage　temperature　(denoted　as　Ts)　of　the　raw　stocks　tanned　with　the　alkyl　sulfonyl　chloride　was　fully　investigated.　The　results　proved　that　the　traditional　leather　tanning　theory　had　obvious　limitations,　and　that　Ts　did　not　increase　with　the　synthetic　oil-tanning　agent,　e.g.,　alkyl　sulfonyl　chloride.　Consequently,　it　can　be　concluded　the　alkyl　sulfonyl　chloride　shows　no　tanning　properties　and　only　serves　the　function　of　fatliquoring.