Ultrafast relaxation dynamics of silver ultrafine particles in aqueous solutions was measured by an ultrafast lensing effect (ULE) method using two types of samples with SDS (sodium dodecyl sulfate) and without SDS. The fit to the ULE time evolution required three exponential components: one for the increase and two others for the decrease. The time constants were estimated as 1, 3, 7 ps for the sample without SDS and as I, 2, and 23 ps for the sample with SDS. The ultrafast relaxation dynamics was discussed in connection with the behavior of photoexcited electrons.