The present invention provides a syringe including a tubular barrel. The tubular barrel has an open proximal end, a distal end with a fluid expelling passage defined therein, and a barrel chamber. A seal is disposed within the barrel chamber a predetermined distance away from the open proximal end in fluid-tight and axially-sliding engagement with the barrel chamber, so that fluid held in the barrel chamber between the fluid expelling passage and the seal can be expelled from the barrel chamber to the outside via the fluid expelling passage by sliding the seal towards the fluid expelling passage. The seal defines at least two diametrically enlarged portions at axially spaced apart portions of the seal so as to be respectively in abutment with the inner wall of the barrel chamber and a concave portion between adjacent diametrically enlarged portions of the at least two diametrically enlarged portions for defining a clearance relative to the inner wall of the barrel chamber, in which lubricant film exists at interfaces between the at least two diametrically enlarged portions of the seal and the inner wall of the barrel chamber, and lubricant is filled in the clearance. The present invention also provides a syringe assembly and an apparatus for manufacturing the syringe having the above arrangement.