This study aimed to determine the extent of and factors associated with delays in streptokinase (SK) administration for ST Segment Elevation Myocardial Infarction (STEMI) patients at emergency department, Rajavithi hospital. Twenty STEMI patients received SK between 2009 and 2013 were recruited. A retrospective study was carried out and data were collected using a screening form. The ethics committee, Rajavithi hospital approved this study. The results revealed that 64.3% of STEMI patient who received late SK (over 30 minutes). Factors associated with delayed in SK administration were the periods since coming to the hospital to get EKG and screening of patients by severity. In the group with delayed in SK administration, it was found that an average amount of time patients came to the hospital to be treated by the EKG was significantly higher than those who were treated timely SK (16.8±30.9 VS 4.4±4.3 minutes: p-value=0.002). For those who were screened as emergency cases, a significantly lower rate of delays in SK administration was found compared to those who were assessed as urgent cases. Gender, age, time of service, characteristics of patients who received services, waiting time to see a doctor, and nurse?s experience to assess patients were not associated with delays in receiving SK. This study determined the reasons of delays in receiving SK in STEMI patients. Pre-hospital, appropriate screening and treatment should provide to STEMI patients as soon as possible early after entering emergency room.