Rapid urbanization and growing kitchen waste generation necessitate the sustainable management of kitchen waste, which has become an important environmental concern. This study investigated the impact of kitchen waste compost and agricultural waste mix on cucumber seedling development. Seven treatments were set up, including a commercial seedling substrate (CK) and six mixes with different ratios of kitchen waste compost, peat, fermented straw, and fermented rice husk (T1~T6), each replicated three times. Results indicated that the substrate with 15% kitchen waste compost, 45% peat, and 40% fermented rice husk (T2) was the most suitable for cucumber seedling growth. This treatment showed significant advantages in leaf area, root length, and fresh and dry weights of aboveground and belowground parts compared to other treatments, though it had relatively higher pH and electrical conductivity (EC) values. The high salt content in kitchen waste compost was identified as a critical factor affecting cucumber seedling growth. Future research should integrate findings on cucumber salt tolerance to further optimize seedling substrates containing kitchen waste compost, ensuring their safe and effective use in agricultural production.