Lobed leaves play a critical role in enhancing the productivity of sprawling crops like zucchini by improving light capture and boosting photosynthesis. However, the genetic basis in zucchini remains largely unknown. Here, we developed an F₂ population from a cross between the entire-leaf cultivar ‘LR’ and the deeply lobed cultivar ‘Xi’. Genetic analysis showed that the non-lobed trait is dominant, with the F₂ segregation ratios (~9 entire:6 shallowly lobed:1 deeply lobed) indicating digenic inheritance. Using bulked segregant analysis sequencing (BSA-seq) and kompetitive allele-specific PCR (KASP) marker analysis, we identified a major effect locus at a 79.8 kb interval on chromosome 10. Within in this interval, gene expression profiling and annotation indicated CpARF6, encoding an auxin response factor, to be the prime candidate gene. Sequencing analysis revealed five nonsynonymous mutations in this gene, including a critical serine-to-leucine substitution at position 335 within the auxin response domain, which is likely a loss function mutation. Our findings establish CpARF6 as a critical regulator of lobed leaf formation in zucchini, providing valuable insights for both leaf development studies and zucchini breeding.