Researchers assess physical activity (PA) to determine both the amount and intensity of activity being performed. Accelerometery has become one of the most widely used methods of assessing PA in large population studies. Pedometers have been used in research for at least 25 years with early studies focusing primarily on validity and reliability. All the validity and reliability studies have been focused on long duration aerobic activities, but there are a few studies on short duration activities. PURPOSE: The purpose of the study was to examine energy expenditure of 3 minutes treadmill exercise that was obtained by activity monitors and ACSM formulas. DESIGN: Thirty collage students participated in the study. VO2max was determined with Astrand-Rhyming sub maximal cycle ergo meter test protocol. Seventy percent (70%) workload of maximal oxygen uptake computed with ACSM's running formulas for each subjects. The subjects were exercised on treadmill in three minutes period, with this computed workload. During treadmill exercise, heart-rate (HR), accelerometer total calori (ATC), accelerometer vector magnitude (VM), pedometer total calori (PC), pedometer step count (ST), result of ACSM's energy expenditure formules (AC), rating of perceived exertion (RPE) were determined for each minute. RESULT: Result of multivariate (ANOVA) test showed that there were significant differences between Accelerometer total calorie, Pedometer calorie and computed (AC) calorie (p=.000). Pearson correlation coefficients for each comparison of subjects were, .132 for ATC and AC, and -.056 for AC and PC, and -.319 for AC and HR, -.072 for AC and RPE, -.046 for ATC and PC, -.265 for PC and HR, .260 for PC and RPE, .070 for ATC and HR, .211 for ATC and RPE. All correlations were not significant (p>0.05). CONCLUSION: There was a significant difference between activity monitors and computed calories by ACSM equations. Correlation coefficients between activity monitors, RPE and the result of ACSM's equation were insignificant. According to these findings that were obtained for 3 minutes duration, these activity monitors and ACSM equations may not give researchers and practitioners similar activity data and may not be interchangeable. It is evident that many researches have been found significant associations between energy expenditure and activity monitors for longer duration exercises more than 3 minutes. Keyword(s): assessment, measurement/evaluation, research