Let (M, d, µ) be a metric measure space with upper and lower densities:where β, β ⋆ are two positive constants which are less than or equal to the Hausdorff dimension of M. Assume that pt(·, ·) is a heat kernel on M satisfying Gaussian upper estimates and L is the generator of the semigroup associated with pt(·, ·). In this paper, via a method independent of Fourier transform, we establish the decay estimates for the kernels of the fractional heat semigroup {e −tL α }t>0 and the operators {L θ/2 e −tL α }t>0, respectively. By these estimates, we obtain the regularity for the Cauchy problem of the fractional dissipative equation associated with L on (M, d, µ). Moreover, based on the geometric-measure-theoretic analysis of a new L p -type capacity defined in M × (0, ∞), we also characterize a nonnegative Randon measureis the weak solution of the fractional diffusion equation (∂t + L α )u(t, x) = 0 in M × (0, ∞) subject to u(0, x) = f (x) in M.