The　crystal　structure,　magnetization,　and　spontaneous　magnetostriction　of　ferromagnetic　Laves　phase　GdFe2　compound　have　been　investigated.　High　resolution　synchrotron　x-ray　diffraction　(XRD)　analysis　shows　that　GdFe2　has　a　lower　cubic　symmetry　with　easy　magnetization　direction　(EMD)　along　[100]　below　Curie　temperature　T-C.　The　replacement　of　Gd　with　a　small　amount　of　Tb　changes　the　EMD　to　[111].　The　Curie　temperature　decreases　while　the　field　dependence　of　the　saturation　magnetization　(M-S)　measured　in　temperature　range　5-300　K　varies　with　increasing　Tb　concentration.　Coercivity　H-C　increases　with　increasing　Tb　concentration　and　decays　exponentially　as　temperature　increases.　The　anisotropy　in　GdFe2　is　so　weak　that　some　of　the　rare-earth　substitution　plays　an　important　role　in　determining　the　easy　direction　of　magnetization　in　GdFe2.　The　calculated　magnetostrictive　constant　lambda(100)　shows　a　small　value　of　37x10(-6).　This　value　agrees　well　with　experimental　data　30x10(-6).　Under　a　relatively　small　magnetic　field,　GdFe2　exhibits　a　V-shaped　positive　magnetostriction　curve.　When　the　field　is　further　increased,　the　crystal　exhibits　a　negative　magnetostriction　curve.　This　phenomenon　has　been　discussed　in　term　of　magnetic　domain　switching.　Furthermore,　magnetostriction　increases　with　increasing　Tb　concentration.　Our　work　leads　to　a　simple　and　unified　mesoscopic　explanation　for　magnetostriction　in　ferromagnets.　It　may　also　provide　insight　for　developing　novel　functional　materials.