Fluctuation is observed by measuring the time series data of ac conductivities at 2 kHz for the \(c\)-axis of the isomorphic rare-earth nitrate crystals of the formula R(NO3)36H2O where R is a rare-earth element (R = 57La, 58Ce, 59Pr, 60Nd, 62Sm, 63Eu, 64Gd, 65Tb, 66Dy, 67Ho, 68Er, 69Tm, 70Yb, and 71Lu). The variation in the structure of the fluctuation is found by changing the rare earth element in the crystals at 16, 30, and 50 K. Singularities in the fluctuation are observed in the 63Eu and 64Gd for the rare-earth element sequence of these crystals.