The community structures and seasonal changes of soil microarthropods were investigated in a natural Sessile Oak (Quercus petraea) stand and adjacent Scots Pine (Pinus sylvestris) plantation located in the Belgrad Forest of Istanbul. Soils for microarthropods were sampled monthly using steel soil corers between November 2008 and October 2009. Soil fauna samples were extracted with a modified Berlese-Tullgren funnel and stored in 70% ethanol. A total of 26 taxons of microarthropods were identified in the oak stand and Scots pine plantation. The mean annual number of microarthropods per square meter was 42.851 for the oak stand versus 42.276 for the Scots pine plantation. The Collembola and Acarina are the two dominant taxa in numbers constituting 94% and 93% of all soil microarthropods of the native oak and Scots pine plantation, respectively. The Shannon diversity index (H') of microarthropods in the Scots pine site (1.72) was found significantly (P=0.008) higher than those of the native oak (1.57). This result implies that even though conversion of Sessile oak land to a Scots pine plantation may decrease the abundance but increased the diversity of soil microarthropods.