The micellar dynamics of many (PEO-PPO-PEO) triblock copolymers have been extensively investigated throughout the past decade using ultrasonic relaxation or temperature jump experiments. These methods primarily use the total scattering intensity-to quantify the exchange mechanisms, and these results are then interpreted to get an idea about temporal evolution of the micelle size and size distribution. In this paper, we present experiments where we directly measure the size of the micelles and the size distribution during the exchange kinetic of the pluronic triblock copolymer P103. Solutions of the commercial P103 surfactant form premicelle aggregates in the proximity of the critical micelle temperature and proper micelles at high temperatures. The kinetics of evolution from aggregates to proper micelles is investigated using dynamic light scattering after a temperature jump. The temporal evolution of the scattering intensity and the average size as well as the size distribution were used to discuss the possible exchange mechanisms.