Abstract: Rice leaf inclination is an important agronomic trait, closely related to plant architecture and yield. Identification of genes controlling leaf inclination would assist in crop improvement. Although various factors, including the plant hormones auxin and brassinosteroids, have been shown to regulate lamina joint development, the role of microRNAs in regulating leaf inclination remains largely unknown. Here, we functionally characterize the role of rice miR394 and its target, LEAF INCLINCATION 4 (LC4), which encodes an F-box protein, in the regulation of leaf inclination. We show that miR394 and LC4 work, antagonistically, to regulate leaf lamina joint development and rice architecture, by modulating expansion and elongation of adaxial parenchyma cells. Suppressed expression of miR394, or enhanced expression of LC4, results in enlarged leaf angles, whereas reducing LC4 expression by CRISPR/Cas9 leads to reduced leaf inclination, suggesting LC4 as candidate for use in rice architecture improvement. LC4 interacts with SKP1, a component of the SCF E3 ubiquitin ligase complex, and transcription of both miR394 and LC4 are regulated by auxin. Rice plants with altered expression of miR394 or LC4 have altered auxin responses, indicating that the miR394-LC4 module mediates auxin effects important for determining rice leaf inclination and architecture.