  Let $(M, g)$ be a smooth n-dimensional Riemannian manifold for $n\ge 2$.
Consider the conformal perturbation $\tilde{g}=h g$ where $h$ is a smooth
bounded positive function on $M$. Denote by $\tilde{p}_t(x,y)$ the heat kernel
of manifolds $(M, \tilde{g})$. In this paper, we derive the upper bounds and
gradient estimates of $\tilde{p}_t(x,y)$.
