The transmembrane region of the protein is likely to have-
A stretch of hydrophilic amino acids
A stretch of hydrophobic amino acids
A disulphide loop
Alternating hydrophilic and hydrophobic amino acids
The transmembrane proteins lie similar to that of the lipid bilayer. The lipid bilayer is hydrophilic in the outer and the inner parts and has a hydrophobic core. 
Similarly, the transmembrane proteins have outer and inner ends which are hydrophilic and a core which is hydrophobic. 
So the transmembrane region of the protein is hydrophobic.