Background <p>Subcutaneous injection is a practice frequently used by nurses and may result in complications.</p> Aim <p>The aim of this study was to evaluate the effect of cold needle on pain, injection satisfaction and ecchymosis development in subcutaneous heparin injection.</p> Methods <p>The study was conducted as a prospective, parallel-group, randomised controlled study with single-blind design. Participants were randomly divided into two groups as chilled needle group (<i>n</i> = 30) and control group (standard needle group) (<i>n</i> = 30). Subcutaneous injections were given to the intervention group with a chilled needle at 0–2&#xa0;°C and to the control group with a needle stored at room temperature. Patients were evaluated for ecchymosis for 72&#xa0;h. Post-procedure pain and satisfaction levels were analysed. The Descriptive Characteristics Information Form, Visual Analogue Scale, Patient Satisfaction Form for Injection and Ecchymosis Follow-up Chart were used to collect the data.</p> Results <p>The intervention group had significantly lower pain scores, compared to the control group (21.00 ± 14.46 vs. 33.00 ± 18.03). In addition, the mean injection satisfaction score of the intervention group (86.33 ± 11.29) was significantly higher than the control group (73.00 ± 17.04). In terms of ecchymosis development, higher rates of ecchymosis formation were observed in the control group, compared to the intervention group.</p> Conclusions <p>The findings support that the cooled needle in subcutaneous injection has the potential to reduce pain, increase injection satisfaction and prevent the development of ecchymosis.</p>