Grain morphology, crystal structure and transistor characteristics of pentacene films have been studied using molecular beam deposition under various conditions: growth temperature ranging from −5 to 80 °C and growth rate from 0.15 to 2 nm/min. Grain morphologies observed with atomic force microscopy are categorized into five groups, which are summarized in a phase diagram. Above the growth temperature of 40 °C, many ‘recessed regions’ which extend independently of molecular steps are observed on the film surfaces. Carrier mobilities of the films estimated from transistor measurements are distributed from 1×10−5 to 0.20 cm2/Vs. A comparative study between the structural and electrical results indicates that the mobility does not explicitly depend either on grain size or on specific grain morphology. Lamellar grains associated with flat-lying molecules among differently oriented grains, gaps between grains and the recessed regions are considered to restrict the overall carrier mobility.