This study evaluates three batches consistency, immunity duration and safety of inactivated Enterovirus 71(EV-A71) vaccine(vero cell) post-marketing among children aged 6-35months in China.3000 subjects will be recruited in this study, of who 1500 subjects will be randomly assigned in a ratio of 1:1:1 to receive one of the three batches of EV-A71 vaccines manufactured by 40L capacity reactor, other 1500 subjects will be randomly assigned in a ratio of 1:1:1 to receive one of the three batches of EV-A71 vaccines manufactured by 150L capacity reactor. Vaccine wil be administrated according to a two doses of schedule given at day 0 and 28. Sample will be collected at day 0, day 56 and at month 13 after vaccinaiton.

Inclusion Criteria:

• Healthy children aged 6-35 months
• Subjects who have been clinically judged to be healthy by the researcher after being asked about the medical history and related physical examination
• The subjects' guardians agree the requirements of the protocol and the relevant follow up visits
• The subjects' guardians agree and sign the informed consent
• Subjects who have no relocation or long-term travel plan within one year and are able to comply with the requirements of the clinical trial protocol.

Exclusion Criteria:

• Subject who has a medical history of HFMD caused by EV71 or has been vaccinated with EV71 vaccine
• Subject that has a history of allergies to vaccines or vaccine ingredients, and has serious side effects on vaccines, such as allergies, urticaria, dyspnea, vascular neuroedema or abdominal pain
• Subject who has congenital malformations or developmental disorders, genetic defects, severe malnutrition, etc.
• Subject who has a history of epilepsy, convulsion or convulsion, or a family history of mental illness
• Subject who has autoimmune disease or immune deficiency, or whose parents and siblings have autoimmune disease or immune deficiency
• Subject who has a history of asthma, vascular and neuroedema, diabetes or malignant tumor
• Subject who has a thyroid resection history, or received treatment due to thyroid disease in the past 12 months
• Subject who has an abnormal coagulation function (such as coagulation factor deficiency, coagulant disease, platelet abnormality) or obvious bruising or clotting disorder which was diagnosed by doctors.
• Asplenia, functional asplenia, or splenectomy due to any circumstances
• Acute onset of various acute or chronic diseases in the last 7 days
• Immunosuppressant therapy, antiallergic therapy, cytotoxicity therapy, inhaled corticosteroids (excluding corticosteroid spray therapy for allergic rhinitis, surface corticosteroid therapy for acute non-dermatitis) in the past 6 months
• Any prior administration of blood products in last 3 months
• Any prior administration of other research medicines or vaccines in last 1 month
• Any prior administration of attenuated live vaccine in last 15 days
• Any prior administration of subunit or inactivated vaccines in last 7 days
• Under the anti-TB prevention or therapy
• Underarm temperature > 37.0 ℃ for fever before vaccination
• Other factors that are not suitable for clinical trials according to the judgment of researchers

Exclusion Criteria for the second dose:

• Have severe allergic reaction after first dose
• Have severe adverse reactions related to first dose
• Any situation meet the exclusion criteria stated in the exclusion criteria for first dose
• Acute infection or illness
• Other factors that are not suitable for clinical trials according to the judgment of researchers