In this paper we study the page number of upward planar directed acyclic graphs. We prove that the page number of any upward planar directed acyclic graph G is a function of the page number of a four-connected subgraph of G; further, we provide an upper bound on the page number of G if G has small diameter; finally, we show that every upward planar directed acyclic graph has small page number if and only if every upward planar directed acyclic graph with small degree does.