1852 saw an influx of English and American missionaries into Siam as Mongkut hired them to teach the English language to the princess. He also hired Western mercenaries to train Siamese troops in Western style. In Bangkok, American Dan Beach Bradley had already reformed the printing and then resumed the publishing of Siam's first newspaper, the Bangkok Recorder. However, the missionaries were not as successful when it came to making religious conversions.
However, Mongkut did not abandon the traditional culture of Siam. In 1852, he ordered the nobles of the court to wear upper garments. Previously, Siamese nobles were forbidden to wear any shirts to prevent them from hiding any weapons in it and met the king bare-chested. The practice was criticized by Westerners and so Mongkut ended it.
For Buddhism, Mongkut pioneered the rehabilitation of various temples. He also began the Magha Puja (มาฆบูชา) festival in the full moon of the third lunar month, to celebrate Buddha's announcement of his main principles. He instigated the Recompilation of Tripitaka in Siam according to Theravada traditions. He also formally established the Thammayut sect as a rightful branch of Theravada.
Mongkut also improved women's rights in Siam. He released a large number of royal concubines to find their own husbands, in contrast to how his story has been dramatized. He banned forced marriages of all kinds and the selling of one's wife to pay off a debt.
In contrast to the previous king, Nangklao, Mongkut didn't see the importance of sending envoys to the Qing dynasty court, as the mission symbolised Siam's subjection to the Qing emperors and because the Qing dynasty was then not so powerful as it had once been, as it was itself threatened by Western powers.