Abstract: This study proposed the use of adaptively adding secondary units in adaptive cluster sampling when the primary units are formed by a spatial cluster of secondary units. Adaptive cluster sampling with this recommended approach of adaptively adding units is called adaptive cluster sampling with spatially clustered secondary units. The purpose of adaptive cluster sampling with spatially clustered secondary units is to provide efficient estimators and to save time and cost of travelling and observing units in the sample. For this sampling design, each primary unit is divided into four secondary units. An initial sample of primary units is selected and then secondary units are adaptively added to the sample instead of neighboring primary units. This study offers an unbiased estimator of the mean and its variance and shows the advantages and disadvantages of adaptive cluster sampling with spatially clustered secondary units in comparison to the ordinary adaptive cluster sampling based on a simple random sample.