“…This paper is concerned with the Cauchy problem for a nonlinear fractional diffusion equation 1) where N ≥ 1, ∂ t := ∂/∂t, (−∆) θ/2 is the fractional power of the Laplace operator with 0 < θ < 2, p > 1 + θ/N and ϕ ∈ L ∞ (R N ) ∩ L 1 (R N ). We say that a continuous function u in R N × (0, ∞) is a solution of (1.1) if u satisfies u(x, t) = Problem (1.1) appears in the study of nonlinear problems with anomalous diffusion and the Laplace equation with a dynamical boundary condition and it has been studied extensively by many mathematicians (see [1], [6], [7], [10], [11], [14], [17], [18], [24] and references therein). Among others, Sugitani [24] showed that, if 1 < p ≤ 1 + θ/N , then problem ( (See [17] and [18].)…”