Crime scenes contain biological evidence such as blood, semen and saliva. This kind of evidence involves DNA. Using DNA analysis, the connection between the suspect-victim-crime triangle is resolved. Therefore, it’s important to collect enough DNA from crime scenes. Cotton swabs are often used in crime scenes to collect evidence. All these years there has been only one swab used in crime scene investigations, but since the late 90’s the double swab technique has been preferred by many crime scene investigators. Nevertheless, the double swab technique hasn’t been approved. However, some studies showed the double-swab technique is more efficient than the single swab technique. The aim of the study is to determine the amount of DNA increment by the double swab technique on parquet and tile surfaces. In this study, a representative crime scene was made. Bloodstains were made on parquet and in between two tiles. After spotting blood on parquet and tiles; each stain was swabbed with a damped cotton swab. After all samples collected with damped swabs, each sample was collected with a second damped swab. DNA extraction was performed with the QIAamp DNA Investigator Kit - QIAGEN from these separately collected biological samples, and then the amount of DNA obtained was measured with the Qubit 4 Fluorometer-Thermo Fisher Scientific.According to the DNA results obtained from the blood samples taken from the floor and tiles with the double swab technique, it has been shown that at least as much DNA as the first swab can be reached in the second swab, and sometimes even more DNA can be obtained. Keywords: Forensic science, forensic biology, crime scene, collection of biological samples, swabs, double-swab technique