Antibodies　have　been　increasingly　used　as　pharmaceuticals　in　clinical　treatment.　Thermal　stability　and　unfolding　process　are　important　properties　that　must　be　considered　in　antibody　design.　In　this　paper,　the　structure-encoded　dynamical　properties　and　the　unfolding　process　of　the　Fab　fragment　of　the　phosphocholine-binding　antibody　McPC603　are　investigated　by　use　of　the　normal　mode　analysis　of　Gaussian　network　model　(GNM).　Firstly,　the　temperature　factors　for　the　residues　of　the　protein　were　calculated　with　GNM　and　then　compared　with　the　experimental　measurements.　A　good　result　was　obtained,　which　provides　the　validity　for　the　use　of　GNM　to　study　the　dynamical　properties　of　the　protein.　Then,　with　this　approach,　the　mean-square　fluctuation　(MSF)　of　the　residues,　as　well　as　the　MSF　in　the　internal　distance　(MSFID)　between　all　pairwise　residues,　was　calculated　to　investigate　the　mobility　and　flexibility　of　the　protein,　respectively.　It　is　found　that　the　mobility　and　flexibility　of　the　constant　regions　are　higher　than　those　of　the　variable　regions,　and　the　six　complementarity-determining　regions　(CDRs)　in　the　variable　regions　also　exhibit　relative　large　mobility　and　flexibility.　The　large　amplitude　motions　of　the　CDRs　are　considered　to　be　associated　with　the　immune　function　of　the　antibody.　In　addition,　the　unfolding　process　of　the　protein　was　simulated　by　iterative　use　of　the　GNM.　In　our　method,　only　the　topology　of　protein　native　structure　is　taken　into　account,　and　the　protein　unfolding　process　is　simulated　through　breaking　the　native　contacts　one　by　one　according　to　the　MSFID　values　between　the　residues.　It　is　found　that　the　flexible　regions　tend　to　unfold　earlier.　The　sequence　of　the　unfolding　events　obtained　by　our　method　is　consistent　with　the　hydrogen-deuterium　exchange　experimental　results.　Our　studies　imply　that　the　unfolding　behavior　of　the　Fab　fragment　of　antibody　McPc603　is　largely　determined　by　the　intrinsic　dynamics　of　the　protein.