Steady adhesion under varying humidity conditions is fundamentally challenging due to the barrier of interfacial water molecules. Here, we demonstrate a humidity-resistant gecko-inspired microfibrillar adhesive fabricated by using a specific phenyl-rich polysiloxane. In contrast with the great decline of macroadhesion with increasing humidity for the typical polydimethylsiloxane (PDMS) microfibrillar adhesives, strong macroadhesion of a microfibrillar adhesive fabricated using synthetic phenyl-rich polysiloxane maintains adhesion well across a wide relative humidity range (1% to 95%). Moreover, the pull-off strength is increased by 500% compared to that of phenyl-absent PDMS microfibrillar adhesives at extremely high humidity. Mechanism analysis demonstrates that the synergistic interplay of strong interfacial hydrophobicity leading to dry contact and bulk energy dissipation through massive aromatic π-π interactions contributes greatly to the reliable and strong humidity macroadhesion. The present results provide a better understanding of humidity macroadhesion as well as application potential for microfibrillar adhesives, which are proven to be reliable skin adhesive patches for long-term health-care that have to be exposed to varying humidity conditions of the skin surface.