Hypertrophic obstructive cardiomyopathy (HOCM) is a well-recognized inherited cardiac disease. This study was conducted to explore the role of lncRNA ADAMTS9 antisense RNA 1 (ADAMTS9-AS1) in HOCM-induced cardiomyocyte hypertrophy. The serum of HOCM patients was collected. AC16 cells were treated with isoproterenol (ISO) and transfected with oe-ADAMTS9-AS1 vector, miR-185-5p mimic, and lysine acetyltransferase 7 (KAT7) specific small interfering RNA. lncRNA ADAMTS9-AS1, miR-185-5p, KAT7, brain natriuretic peptide (BNP), and atrial natriuretic peptide (ANP) in the serum or cells were determine by qRT-PCR or Western blot assay. Cell surface area was observed by Texas Red-Phalloidin staining. Subcellular localization of lncRNA ADAMTS9-AS1 was tested by nuclear/cytoplasmic fractionation assay, with RNA pull-down and dual-luciferase assay to validate gene interactions. lncRNA ADAMTS9-AS1 was downregulated in the serum of HOCM patients and ISO-treated AC16 cells. lncRNA ADAMTS9-AS1 overexpression inhibited ISO-induced cardiomyocyte hypertrophy and reduced levels of ANP and BNP. lncRNA ADAMTS9- AS1 was located in cytoplasm and inhibited miR-185-5p expression through targeted binding. miR-185-5p bound to KAT7 3'UTR and inhibited KAT7 expression. miR-185-5p overexpression and KAT7 knockdown both neutralized the inhibitory role of lncRNA ADAMTS9-AS1 in cardiomyocyte hypertrophy. Overall, lncRNA ADAMTS9-AS competitively bound to miR-185-5p to up-regulate KAT7 and thus inhibited cardiomyocyte hypertrophy.