Abstract: Background and Objective: In Egypt, onion is an important and economical crop it needs good seedbed preparation to achieve the optimum growing conditions. The present investigation aimed to study the effect of using different seedbed preparation methods on some engineering properties of onion which affect its quality and yield. Materials and Methods: The experiments were carried out during the agricultural season of 2015-2016 in Giza governorate. Onions (Allium cepa) L. Beheri (red) cultivar were transplanted manually at late December, 2015 in the winter planting season under surface irrigation. Two main treatments were compared. First treatment includes three tillage systems: The new combined machine (NCM), conventional method system (TM) and no tillage treatment (NT). Second treatment was done with three different soil moisture contents at plowing (SMC), SMC1 = 9.5%, SMC2 = 18%, SMC1 = 23%, respectively. Data were analyzed by one-way ANOVA using SAS. Results: The obtained results showed clearly that all engineering properties of onion bulb had a positive response with tillage systems: The lowest geometric mean diameter Dmg (cm) and arithmetic mean diameter Dam were obtained under using NCM. On the other hand, the highest value was obtained under NT. The highest cross- section area ACS and the lowest one were obtained in NT system and NCM, respectively. The increase in soil moisture stress in the root zone has a depressive effect on cross- section area ACS. Shape index showed adverse effect where the highest value 0.81 was obtained under 9.5% soil moister content. The lowest of ACS and shape index were obtained under q2 and q3, respectively. The volumes of bulb onion were affected with soil moisture content where increasing soil moisture content decreased volumes of bulb onion. Conclusion: All engineering properties of onion bulb had a positive response with tillage systems.