Triple-negative　breast　cancer　(TNBC)　is　the　most　lethal　subtype　of　breast　cancer　and　significantly　associated　with　poor　prognosis　and　high　risk　of　recurrence.　miR-34a　has　been　identified　as　a　potent　tumor　suppressor　whose　expression　is　dramatically　downregulated　in　TNBC.　Currently,　rectification　of　miRNA　abnormality　serves　as　a　novel　tumor　therapeutic　strategy.　miR-34a　is　thus　used　as　powerful　antitumor　agent　for　miRNA-based　therapy　against　TNBC.　However,　miRNA-based　antitumor　therapy　is　challenged　by　effective　targeted　delivery　of　miRNA.　In　the　present　study,　nanodiamond　(ND),　protamine　(PS)　and　folic　acid　(FA)　were　used　to　construct　ND-based　layer-by-layer　nanohybrids　through　a　self-assembly　approach　for　targeted　miR-34a　delivery　in　TNBC　cells　and　xenograft　TNBC　tumors.　We　found　that　the　targeted　delivery　of　miR-34a　remarkably　suppressed　cell　proliferation,　migration　and　induced　the　apoptosis　of　TNBC　cells　in　vitro　and　inhibited　tumor　growth　in　vivo　via　down-regulating　Fra-1　expression.　The　data　suggest　a　great　potential　of　ND-based　nanohybrids　for　targeted　intratumoral　delivery　of　miR-34a　for　TNBC　therapy.