He showed a stronger interest in mathematics, so he quit the Polytechnic University in 1929, despite already having passed all the third-year exams.

In 1932 he returned to Iași, where he remained for almost 10 years, developing a close relationship with professor Alexandru Myller.

He taught the first modern algebra course in Romania, named Logic and theory of proof, at the University of Iași.

During that time, he started writing a series of papers based on the works of Jan Łukasiewicz in multi-valued logic.

His research in mathematical logic laid the foundation for significant work done afterwards in Romania, as well as Argentina, Yugoslavia, Czechoslovakia, and Hungary.

While in Iași, he completed research remarkable for the many new ideas and for his way of finding and using new connections between concepts from different areas of mathematics.

Moisil approached the Ministry of Education, arguing that it would be a great opportunity for mathematics in Romania if all four could be appointed.

He developed a multi-dimensional extension of Pompeiu's areolar derivative, and studied monogenic functions of one hypercomplex variable with applications to mechanics.

Furthermore, several of Moisil’s books had an impact on the beginning of computer science: Încercări Vechi și Noi în Logica Neoclasică [New and Old Approaches in Neoclassic Logic], 1953; Teoria Algebrică a Mecanismelor Automate [Algebraic Theory of Automata], 1959; and Circuite cu Tranzistori [Transistorized Circuits], 1961.