Researchers　in　cryogenic　magnetic　refrigeration　have　never　stopped　pursuing　magnetic　refrigerants　with　lower　ordering　temperatures　and　larger　magnetocaloric　effects.　Rare　earth　borates　have　been　found　to　be　potential　cryogenic　magnetocaloric　materials　due　to　their　low　phase　transition　temperatures　and　considerable　magnetic　entropy　changes.　Here,　two　rare　earth　borates　RE8.66(BO3)(2)(B2O5)O-8　(RE　=　Er,　Tm)　were　successfully　fabricated,　and　the　crystallographic　and　magnetic　parameters　as　well　as　cryogenic　magnetocaloric　effects　were　systematically　evaluated.　The　compounds　are　deemed　to　crystalize　in　a　monoclinic　structure　belonging　to　space　group　C2/m.　They　are　both　second-order　phase　transition　materials　without　any　long-range　order　above　2　K.　These　monoclinic　rare　earth　borates,　especially　for　Er-8.66(BO3)(2)(B2O5)O-8,　show　more　considerable　low-field　magnetocaloric　effects　than　rare　earth　orthoborates.　For　&　UDelta;H　=　1　and　2　T,　the　values　of　-&　UDelta;　S　M　max　are　5.1　and　11.2　J/(kg　K)　for　Er-8.66(BO3)(2)(B2O5)O-8,　3.0　and　5.3　J/(kg　K)　for　Tm-8.66(BO3)(2)(B2O5)O-8,　respectively.　Therefore,　they　are　regarded　as　potential　candidates　for　cryogenic　magnetic　refrigeration.