Positive reinforcement occurs when a reward, sometimes called a reinforce, is given for a specific desired behavior. It can be a tangible object, an activity, something sensory, or social. Pain is a subjective experience, and no objective tests exist to measure it. Vein puncture is one of the most painful medical procedures for a child, and it is one of the most frequently performed procedures. The study aimed to evaluate the contribution of positive reinforcement in reducing children's pain responses during vein puncture. Quasi experimental design was conducted for this study. It was conducted in the medical unit of El- Menuofyia and Tanta university hospitals. Eighty children's accompanied by a female care givers, were selected according to specific criteria. After collecting demographic data, the type of reinforcer was chosen after observation and interview. It was individualized according to children preference and motivation. It was consistently delivered after a desired behavior. Reinforcer was administered immediately after a desired behavior, and after simple explanation for to the child. Data collection regarding pain was started after 4 consecutive use of positive reinforcement of a desired behavior in other procedures. Reinforcer was used to observe children' pain during vein puncture and to evaluate the effect of positive reinforcement on children FLACC , Wong -Baker faces, heart rate and oxygen saturation. The caregivers "mothers" were involved in all steps of data collection. The result of the study showed that High statistical significant differences were found regarding FLACC Scale -Pain Assessment Tool- "Observer Rated Pain Scale and Wong Baker Scale before and after reinforcement. In relation to pulse and oxygen saturation there was statistical significant difference during vein puncture. According to the current study, it is recommended to replicate the study with a larger sample size in children undergoing other painful procedure. and developing an educational program for nursing staff to increase the skills of positive reinforcement of well or healthy behaviors of children.