Background and aims: During recent decades, bed rest is prescribed as a traditional treatment for many musculoskeletal disorders, which is today being challenged in terms of its efficiency.The present study was aimed to study comparatively the effect of different durations of complete bed rest (CBR).Methods: In this clinical trial study, patients admitted to Ayatollah Kashani Hospital Clinic for acute low back pain were assigned to two groups A=40 and B=80 after homogenization. Group A was treated with celecoxib 200 mg daily and Group B with celecoxib 200 mg daily alongside CBR. Group B began daily activities after recovery from acute low back pain with any amount of CBR. Both groups were examined at enrollment, the third day, the seventh day, and the fourteenth day and standard Mcgill pain questionnaire was filled out for them.Results: According to the findings of this study, total mean pain, based on the score of Mcgill questionnaire, in four examinations in CBR group decreased from 25.5 to 18.6, 9.8, and 2.2, which is statistically significant in all four examinations (p<0.05). In addition, pain decrease in control group was from 24.6 to 21.3, 14.4, and 7.3, with a statistically significant difference in only two (second and third) examinations (p<0.05). Generally, the decrease in pain in CBR group was higher than that in control.Conclusion: The present study indicated that CBR could cause low back pain in the patients with acute low back pain to decrease, with a significant difference from the decrease in pain in only pharmacologic treatment group. As a result, CBR could be suggested as an appropriate supplementary treatment alongside pharmacologic treatment.