In　order　to　improve　the　safety　level　of　mountainous　two-lane　highway,　this　paper　investigated　the　relationship　between　highway　geometric　features　and　rear-end　crash　incidence.　By　using　negative　binomial　generalized　models　and　separating　the　139　kilometers　highway　segment　into　94　successive　vertical　slope　units,　the　statistical　software　Stata9.0　was　used　to　evaluate　the　effects　of　8　variables　which　were　based　on　roadway　geometric　characteristics　on　the　incidence　of　rear-end　crashes　occurred　from　2003　to　2005　on　mountainous　two-lane　highway　in　Gansu　Province.　Unrelated　geometric　variables　were　dropped　one　by　one　by　using　step　regressing　method.　Finally,　the　variables　found　to　influence　the　incidence　of　rear-end　crashes　significantly　was　accumulated　vertical　slope　length.　The　regression　analysis　results　suggest　that　there　are　strong　positive　relationship　between　the　incidence　of　rear-end　crashes　and　accumulated　vertical　slope　length.　So　it　is　wise　to　avoid　too　long　successive　down　slope　when　designers　are　engaged　in　fresh　highway　designs　on　considering　safety　effect.　Copyright　ASCE　2009.