Experimental investigations of the development of transient jets and evolving jet diffusion flames have been made utilizing a high-speed Schlieren visualization. Jet tip penetration velocities and normalized jet widths of the primary vortex have been measured. It is shown that the development behavior in the presence of a flame is greatly different from that in a transient jet. The discernible differences are the delay of the roll-up of the primary vortex, the faster spreading after the roll-up due to the exothermic expansion, and the survival of only a primary vortex. It is also found that the jet tip penetration velocity varies with downstream distance and an increase in Re-s gives rise to a higher tip penetration velocity. The flame response, obtained by a compensated measurement of maximum flame temperature, is examined at two conditions: for the slowly varying strain rate and the case of flame extinction. The flame responses are then analyzed to depict similarities between a stagnant point diffusion flame and an evolving jet diffusion flame. The flame of the slowly time-varying strain rate makes a quasi-steady response. For the case of flame extinction, an unsteady effect of flame response is shown.