If I have done my diploma after 12th can I join iit or  not?

Hi, You are not eligible to take admission in NIT but you are eligible for IIT. Diploma holders are eligible to get direct admission in second year of B.Tech or B.E. through LEET exam. LEET exam is conducted for Diploma holders who want to get admission in B.E or B.tech courses. This is national level exam. But you can also apply for state level exam. Good Luck.