This study aimed at investigating the effectiveness of a developmental group guidance program in career planning for a sample of tenth grade students in the sultanate of Oman. The subjects consisted of (70) students distributed into two groups: a control group (n=35) and an experimental group (n=35). The developmental group career guidance program was used with the experimental group; while the control group did not receive any kind of treatment. The career planning inventory of 48 items and six dimensions developed by (Al-Shezawi, 2017) was admimistered to the subjects. t-test findings showed statistically significant differences in the posttest between the control group and the experimental group in favor of the experimental group. Results of the t-test showed statistically significant differences between the pretest and posttest of the experimental group in favor of the posttest. The study concluded with some suggestions and recommendations in light of findings.