Hydrophobically-modified hydrogels of poly(methacrylic acid) (P(CC16-MAA) were prepared by the free radical copolymerization of methacrylic acid (MAA) and diallyl methyl hexadecyl ammonium salts (CC16) in aqueous solution. The presence of hydrophobic segments could reduce or increase the degree of swelling significantly at low or high pH, respectively. DSC results indicated that crystalline behavior of poly(diallyl methyl hexadecyl ammonium) salts easily took place in the side chain. The gels showed swelling behaviors that were more sensitive to pH change than PMAA hydrogels and PMAA hydrogels hydrophobically-modified by poly(acrylic acid-2-ethylhexyl ester) (P(AAEHE-MAA)). These properties suggest that P(CC16-MAA) is a potential system suitable for drug delivery.