A syringe assembly includes a plunger assembly, a syringe body, and a needle. The plunger assembly includes a plunger rod, a spring, a plunger base, and a plunger plug. The plunger rod includes a first end member having a first stepped part positioned in an inner wall thereof, a second end member, and a first accommodating room. The plunger base includes a plunger body, a projection, a second stepped part, a plunger member, and a locating member. The plunger body is received in the first accommodating room, and the projection abuts against the first end member. The spring is arranged around the plunger body and positioned between the first stepped part and the second stepped part. The plunger plug is mounted to the second end member, and defines a fixing groove. The syringe body includes a needle cannula, a needle base, a fixing pole, and a fixing valve. The plunger assembly is received in the needle cannula. The needle base is mounted to the needle cannula. The fixing valve is received in the needle base. The fixing pole is received in the fixing valve and protrudes out of the needle base. The needle is received in the fixing pole. The syringe assembly of the present invention is prevented from reuse and accidently damage because the needle can retract into the plunger rod using restoring force of the spring.
