Objective: This study aimed to compare the bactericidal effect of Nd: YAG laser and sodium hypochlorite solution. Background: It is very important to obtain the best sterilization and antibacterial effect during treatment of the infected root canals. Materials and methods: Bacterial samples were taken from infected root canals immediately after the tooth extraction. The samples were divided into 3 groups, each group contained 30 individuals. In the first group, sodium hypochlorite was used alone as a bactericidal agent. In the second group, Nd: YAG laser was used as a bactericidal agent. In the third group, both of them were used. Bacterial swabs were taken from these samples before and after treatment by each bactericidal agent, these swabs were streaked on blood agar and incubated, and the number of the colony forming units was recorded. The diameter of the non-growth zone was measured after exposure to each bactericidal agent. Results: The results showed an excellent bactericidal effect for the sodium hypochlorite group. The number of colony forming units was reduced to about 89% from the original number before the treatment. While the Nd: YAG laser exhibited a weak bactericidal effect with about 25% of the bacterial cells eradicated. The best antibacterial activity obtained was when both sodium hypochlorite and Nd: YAG laser were used together, with a percentage of reduction of about 96%. Conclusion: The sodium hypochlorite has a very good bactericidal action if compared to Nd: YAG laser. The Nd: YAG laser was merely effective as a bactericidal agent. The best bactericidal effect was observed when both sodium hypochlorite and Nd: YAG laser were used together. Nd: YAG could be used as a co-adjunctive agent to agitate the sodium hypochlorite solution and to increase its activity.