Different　storage　capacities　and　various　file　sizes　are　two　crucial　factors　which　impact　the　effectiveness　of　cache　placement　in　device-to-device　networks.　However,　most　of　existing　literature　assumes　all　users　have　homogeneous　cache　capability　and　all　involved　file　sizes　are　identical.　In　this　paper,　files　are　placed　into　groups　according　to　their　different　sizes　and　the　storage　capacities　are　various　among　all　the　involved　user　devices.　Considering　these　two　vital　factors,　group　caching　scheme　(GCS)　algorithm　for　the　optimal　cache　strategy　is　investigated　by　formulating　an　optimization　problem　to　maximize　the　cache　hit　probability　solved　by　using　Karush-Kuhn-Tucker　conditions.　Furthermore,　random　linear　network　coding-based　GCS　is　developed　to　eliminate　the　negative　impact　of　file　size　to　cache　hit　probability　due　to　the　observation　that　the　probability　of　small　size　files　being　cached　may　be　higher　than　that　of　large　size　but　more　popular　files.　Finally,　simulation　results　show　the　effectiveness　of　the　proposal　which　outperforms　the　existing　schemes.　©　2013　IEEE.