Abstract: Residue cluster play essential role in stabilizing protein structures in the form of a complex network. Considering the anisortopy of 20 amino acids, atom distance criteria (ADC) method is proposed for determination of residue sidechains contact. According to the local clustering coefficient, residue clusters can be classified either as close contact cluster or open contact cluster. Statistical analysis reveals that close contact clusters are the residue cores stabling secondary structures. Whereas most of open contact cluster are bridges connecting neighbor clusters. It is shown that the residue contact network is scale-free distributed and the cluster size is more like a log-normal distribution. The analysis of average cluster size for 424 PDB reveal that protein structures have a critical size at which proteins can be considered as well-condensed.