Pyridyl substituted 1,3,5-triazines are synthesized via an unprecedented one step cyclocondensation from 4H-pyrido[1,3]oxazin-4-ones with amidines, at room temperature or under microwave irradiations, in good to excellent yields. The broad applicability was demonstrated by 33 examples with a variety of amidines and three different 4H-pyrido[1,3]oxazin-4-one chemical series. In addition, a one-pot process from 4H-pyrido[1,3]oxazin-4-ones' precursors (imides sodium salt) was developed and led to the desired triazines compounds, thus allowing a one step economy in their global synthetic preparation. This approach opens a rapid access to pyridyl (or pyridone) substituted 1,3,5-triazines with high potential in various fields of applications.