Aim of the study: Mechanical neck pain is a type of pain that affects the entire neck or shoulder area, that is characterized by mechanical symptoms such as symptoms triggered by maintained neck postures, neck movements, or palpation of the cervical muscles. Around twothirds of people in their forties and fifties suffer from neck pain. Stretching exercises have many advantages, including enhanced muscle performance and endurance, injury prevention, improved muscle or athletic performance, healing promotion, and a reduced onset of muscle soreness. The hyperactive muscle relaxes well after using the post isometric relaxation procedure. We aimed to compare between the efficacy of passive stretching exercises and post isometric relaxation technique on neck pain severity and functional disability as well as neck sagittal, coronal and transverse mobility in treatment of patients with chronic mechanical neck pain. Methods: Forty male and female patients diagnosed as chronic mechanical neck pain, whose age ranged between 20 to 40 years with duration of illness ranged between 3 and 24 months participated in this study. They were randomly distributed into two equal experimental groups. The first group received passive stretching exercises for upper fibers of trapezius, levator scapulae and sternocleidomastoid muscles and the second group received post isometric relaxation technique for upper fibers of trapezius, levator scapulae and sternocleidomastoid muscles. In addition to that both groups received infrared radiation before each treatment session for warming up. All patients were treated for 12 sessions (3sessions/week) every other day for four weeks. Results: Both groups had significant improvement in all measured variables. Post isometric relaxation technique was significantly more effective than passive stretching exercises in reduction of neck pain severity and functional disability as well as improving neck coronal mobility. However, there was no significant difference between both groups in improving neck sagittal and transverse mobility.