We have produced a thermally stable recombinant human type 5 adenoviral vector (AdHu5) through spray drying with three excipient formulations (l-leucine, lactose/trehalose and mannitol/dextran). Spray drying leads to immobilization of the viral vector which is believed to prevent viral protein unfolding, aggregation and inactivation. The spray dried powders were characterized by scanning electron microscopy, differential scanning calorimetry, Karl Fischer titrations, and X-ray diffraction to identify the effects of temperature and atmospheric moisture on the immobilizing matrix. Thermal stability of the viral vector was confirmed in vitro by infection of A549 lung epithelial cells. Mannitol/dextran powders showed the greatest improvement in thermal stability with almost no viral activity loss after storage at 20 °C for 90 days (0.7 ± 0.3 log TCID50) which is a significant improvement over the current −80 °C storage protocol. Furthermore, viral activity was retained over short term exposure (72 h) to temperatures as high as 55 °C. Conversely, all powders exhibited activity loss when subjected to moisture due to amplified molecular motion of the matrix. Overall, a straightforward method ideal for the production of thermally stable vaccines has been demonstrated through spray drying AdHu5 with a blend of mannitol and dextran and storing the powder under low humidity conditions.