Knee osteoarthritis (KOA) is one of the most common musculoskeletal diseases in clinic. It usually occurs in middle-aged people, especially women. An estimated lifetime risk for KOA is approximately 40% in men and 47% in women. KOA is a chronic disease which can lead to obvious pain, joint stiffness, limitation of activity and even disability, with significant associated costs and effects on society, health systems, and individuals. The use of acupuncture as an approach for the management of chronic pain, is receiving increasing recognition from both the public and professionals. However, there are no universally accepted treatment frequency criteria in previous studies. The number of acupuncture treatments is no more than twice per week in most previous studies, while it is usually 3-5 sessions per week in clinical practice in China. The aim of this study is to compare the effects of different EA sessions (3 sessions per week versus once per week) in a pilot randomized controlled trial of KOA.

Patients will be randomly allocated to one of two groups. In the 24-session treatments group (group A), patients will receive EA 3 sessions per week for 8 weeks. The EA stimulation lasted for 30 minutes with a dilatational wave of 2/100 Hz and a current intensity depending on the participant's comfort level (preferably with skin around the acupoints shivering mildly without pain). It involves having needles inserted into acupoints which are stimulated manually for 10 seconds to create "De Qi" sensation and paired alligator clips will be attached to the needle holders at LR8-GB33 and two other customized acupoints. Disposable needles (Huatuo) and the HANS-200A acupoint nerve stimulator (Nanjing Jisheng Medical Co., Ltd. production) will be used.

Patients in the 8-session treatments group (group B) will receive EA once per week for 8 weeks. Other interventions are the same as group A. Assessments will be conducted at baseline and 4, 6, 8, 12 and 16 weeks after randomization.

It is expected that the interventions will alleviate the sufferings of the patient. The risks of participation are minimal. Occasionally, acupuncture can make people feel nauseous or experience a temporary increase in pain either during or after treatment. Rare side effects during acupuncture treatment include fainting, infection and subcutaneous hematoma (pooling of blood under the skin). Participants will be warned of these potential side-effects before consenting to have acupuncture.

Patients will be allowed, or required, to back out of the trial based on the following:

1. A major protocol violation;
2. Development of a serious disease;
3. Adverse events related to electro-acupuncture;
4. Request to be back out of the trial. The purpose of the study is to accumulate clinical data, obtain the outcome data of the intervention method and prove the feasibility of the study protocol.

Sixty patients will be selected as the sample size according to clinical experience.

Inclusion Criteria:

1. Age 45-75 years old, male or female;
2. Single / bilateral knee pain, duration of more than 6 months;
3. KL (Kellgren-Lawrence) grade Ⅱ or Ⅲ in recent 6 months;
4. NRS ≥ 40mm;
5. Signed informed consent

Exclusion Criteria:

1. Surgery history of knee or waiting for surgery (knee replacement or knee arthroscopy);
2. Knee pain caused by other diseases (such as joint bodies, severe effusion of joint cavity, infection, malignant tumors, autoimmune diseases, trauma, etc.);
3. History of arthroscopy within 1 year or intra-articular injection within 4 months;
4. History of receiving acupuncture treatment within 3 months;
5. Severe acute/chronic organic or mental diseases;
6. Pregnant women, pregnant and lactating women;
7. Coagulation disorders (such as hemophilia, etc.);
8. Participation in another clinical study in the past 3 months;
9. With a cardiac pacemaker, metal allergy or needle phobia.