The purpose of this study was to evaluate in vitro the effects during subgingival calculus removal using Nd:YAG laser. The study group was consisted of 30 teeth with advanced periodontal disease extracted before the start of periodontal therapy. The specimens were divided into 8 different groups : 1) untreated control 2) scaling and root planing only 3) laser treated using 150mJ/pulse, 1sec, 5sec, contact mode 4) laser treated using 200mJ/pulse, 5sec, contact mode 5) laser treated using 150mJ/pulse, 1sec, non-contact mode 6) laser treated using 200mJ/pulse, 5sec, non-contact mode 7) laser treated using l5OmJ/pulse, 1sec, contact mode with water irrigation 8) laser treated using 200mJ/pulse, 5sec, contact mode with water irrigation. All specimens were prepared for evaluation by scanning electron microscopy(SEM). Specimens from Group 2 exhibited a smear layer of scale like texture with parallel instrument tracks resulting from curet use. Specimens treated by contact mode, Group 3 and 4 featured surface changes not observed· in controls such as charring, randomly distributed pitting and crater formation, and melting down of the tooth material and calculus. Specimens treated by noncontact mode, Group 5 and 6 featured similar surface changes observed in contact mode. However, the differences between contact and non-contact groups not significant. Specimens treated by contact mode with water irrigation, Group 7 and 8 featured slight surface change compared to other groups. The results suggested that Nd: YAG laser did not completely remove the subgingival calculus but was possible the application as adjunctive method.