The present study aimed to compare the influence of four different tillage systems on soil characteristics, root system, vegetative growth and seed yield of sunflower. A field experiment was carried out on a clay soil during two consecutive seasons (1999 and 2000) at the Farm of the Agricultural and Water Research Center, Al-Hasa, Saudi Arabia. The suggested land preparation and tillage systems were disc plowing followed by spike tooth harrowing (DPTH), moldboard plowing followed by spike tooth harrowing (MPTH), disc plowing followed by disc harrowing (DPDH), chisel plowing followed by disc harrowing (CPDH) and no tillage  (CONT). The result indicated that there were significant differences between the evaluated systems in soil density at 10 and 20 cm soil depth. DPDH system was superior in producing the lowest values of soil density at both depths and the less soil penetration resistance through the layer of the plowing. All tillage systems increased the initial and basic infiltration rates, compared to the non tillage. Chisel plowing gave the highest initial and basic infiltration rate, while DPDH system gave slightly lower values, compared to chisel plowing but higher than the others. The tillage systems were found to have a significant effect on the root characteristics and plant vegetative growth. Better root length, root distribution area, fresh and dry weight of the root were achieved by DPDH system. There was no significant difference between MPTH and DPTH systems on the root system, except root fresh weight. However, there was a significant difference between DPTH treatment and the others on the root characteristics, except root length. Also, DPDH system resulted in the highest values of the vegetative growth, providing an increase of 28%, 55%, 51% and 70% in plant height, number of leaves per plant, plant  fresh weight and  average leaf area per plant,  respectively compared with  the CONT. No significant differences were existed neither between MPTH and DPTH nor between DPTH and CPDH on the four vegetative parameters. Seed yield and its components of sunflower exposed a significant effect between the various tillage systems. The greatest effect was observed  by DPDH  system which produced the best seed disc  components, giving an increase of 31% in the seed  disc diameter and an 36% in the seed  yield.  It is possibly to suggest  that using the system of  disc plowing followed by disc harrowing could be  the useful land preparation for enhancing the yield of sunflower under the condition of the area of study.