Born in Saitama Prefecture in 1939, Iijima graduated with a Bachelor of Engineering degree in 1963 from the University of Electro-Communications, Tokyo.

He received a Master's degree in 1965 and completed his Ph.D. in solid-state physics in 1968, both at Tohoku University in Sendai.

Between 1970 and 1982 he performed research with crystalline materials and high-resolution electron microscopy at Arizona State University.

He visited the University of Cambridge during 1979 to perform studies on carbon materials.

He was awarded the Benjamin Franklin Medal in Physics in 2002, "for the discovery and elucidation of the atomic structure and helical character of multi-wall and single-wall carbon nanotubes, which have had an enormous impact on the rapidly growing condensed matter and materials science field of nanoscale science and electronics."