Electrostatic interactions of silver colloids with phospholipid monolayers at the air- water interface have been investigated by pressure-area measurements and fluorescence microscopy observations. It has been observed that the presence of silver particles in the subphase induces a change in the compression isotherms of phosphatidylglycerol, in particular in liquid-expanded LE / liquid-condensed LC phase transition. Condensed-phase domains show fractal-like shapes over colloids-containing subphases in contrast with rounded shapes observed over pure water. The effect of colloids on the compressibility was studied for different chain lengths and the change of the critical temperature was also determined. The comparison with the effect of monovalent salt was discussed since the charged colloids could be viewed as "multivalent" ions.