Hypoxia‐inducible factor‐1 alpha (HIF‐1α) is a central transcriptional regulator of hypoxic response. The present study was designed to investigate the role of HIF‐1α in mild hypoxia‐induced cardiomyocytes hypertrophy and its underlying mechanism. Mild hypoxia (MH, 10% O₂) caused hypertrophy in cultured neonatal rat cardiac myocytes, which was accompanied with increase of HIF‐1α mRNA and accumulation of HIF‐1α protein in nuclei. Transient receptor potential canonical (TRPC) channels including TRPC3 and TRPC6, except for TRPC1, were increased, and Ca²⁺‐calcineurin signals were also enhanced in a time‐dependent manner under MH condition. MH‐induced cardiomyocytes hypertrophy, TRPC up‐regulation and enhanced Ca²⁺‐calcineurin signals were inhibited by an HIF‐1α specific blocker, SC205346 (30 μM), whereas promoted by HIF‐1α overexpression. Electrophysiological voltage‐clamp demonstrated that DAG analogue, OAG (30 μM), induced TRPC current by as much as 170% in neonatal rat cardiomyocytes overexpressing HIF‐1α compared to negative control. These results implicate that HIF‐1α plays a key role in development of cardiac hypertrophy in responses to hypoxic stress. Its mechanism is associated with up‐regulating TRPC3, TRPC6 expression, activating TRPC current and subsequently leading to enhanced Ca²⁺‐calcineurin signals.