Although Oura Cathedral is made of brick, white plaster has been applied over the bricks. Its present-day appearance was acquired in 1879 At the time of its foundation, the church was a small church of only three aisles. It had a Gothic-style pointed roof, which had two smaller towers and one larger one, each with a golden cross on top. However, soon after its completion, strong winds caused the two towers at the sides to collapse. The church was also too cramped, so both sides at the front were extended, and they also made the building longer. At the front in the centre is an octagonal spire, which is distinctive. It is the only church in Nagasaki prefecture to have five aisles.

This building tells of the dawn of western-style architecture in Japan. In 1933, Oura Cathedral was designated as a national treasure.