Effects of six tillage practices on some soil microbiological properties and crop yields were evaluated for a clay soil (Typic Haploxererts) under semi-arid Mediterranean conditions in a three year study (2006-2009). The experiment was designed as a completely randomized-block with three replications. Treatments were: conventional tillage with residue incorporated (CT1), conventional tillage with residue burned (CT2), reduced tillage with heavy tandem disc harrow (RT1), reduced tillage with rotary tiller (RT2), reduced tillage with heavy tandem disc harrow for the first crop + no-tillage for the second crop (RNT), and no tillage (NT). The study was conducted in wheat-corn, wheat-soybean and wheat crop rotations. Dehydrogenase activity, soil respiration, mycorrhizal spore number, total organic carbon (TOC), and total N were determined at three depths (0-10, 10-20 and 20-30 cm). The mycorrhizal spore number responded quite early to tillage practices. Significant tillage effects on TOC and total N were observed only at 0-10 cm depth. The TOC content was increased by NT, RT2, RNT and RT1 practices compared to the initial values at the same depth as 74%, 62%, 56%, and 50%, respectively. Dehydrogenase activity (DHA) and soil respiration were higher on the surface and decreased with depth. Reduced and no-tillage practices significantly increased the mycorrhizal spore number, dehydrogenase activity and soil respiration at all depths (P<0.05). Both CT1 and CT2 practices had significant negative effects on all measured soil properties. Tillage practices had no significant effect on crop yields except for the wheat yield in 2008. The results indicated that, as an alternative to conventional tillage, reduced and no-tillage practices provided successful crop production in a clay soil under a semi-arid climate.