Study aim: To compare the efficacy of single dose intraarticular corticosteroid injection and intraarticular low level laser therapy in knee osteoarthritis in terms of pain, osteoarthritis outcomes, quality of life, and adverse events. Design: A phase II, randomized, controlled, parallel group, double blind clinical trial involving 54 patients. Block randomization with a block size of 6 will be performed using Random Allocation Software. Settings and conduct: This clinical trial will be conducted at the Physical Medicine and Rehabilitation Clinic of Firoozgar Hospital, Tehran. Patients will receive either intraarticular injection of 40 mg triamcinolone or intraarticular laser therapy. Procedures will be ultrasound guided, with participant and outcome assessor blinding. Participants/Inclusion and exclusion criteria: Patients aged 45 to 75 years with knee osteoarthritis diagnosed by ACR clinical and radiographic criteria, Kellgren Lawrence grade 2 or 3, and a pain score of at least 4 of 10 will be included. Major exclusions include recent joint injection, surgery or planned arthroplasty, inflammatory or secondary arthritis, bleeding risk, infection, malignancy, diabetes, pregnancy, breastfeeding, relevant medication use, or hypersensitivity. Withdrawal includes withdrawal of consent, new exclusion criteria, loss to follow up, serious adverse events, nonadherence, or protocol violation. Intervention groups: Group A receives ultrasound guided intraarticular triamcinolone acetonide, 40 mg in 1 mL, plus sham laser. Group B receives intraarticular laser therapy, 658 nm, 50 mW, for 20 minutes, delivering 60 J, plus sham injection of 0.5 mL normal saline. Main outcome variables: Pain will be assessed by the Visual Analogue Scale (VAS) and function by the validated Persian Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) at baseline, week 1, and month 1. Adverse events will be recorded.