This study aims at clarifying a relationship between nonisothermal fluid mixing in a T-junction area with a 90-deg bend upstream and temperature fluctuations induced by the unstable mixing, by visualizing the flow fields with particle image velocimetry and measuring fluid-temperature fluctuation in the vicinity of a wall. From the visualization, it is clarified that a high-temperature jet flowing out from a branch pipe swings and sways near the wall, though the mixing patterns are basically classified into the same ones without the 90-deg bend upstream. Furthermore, there are cautionary conditions in which the temperature fluctuation is maximized in a transition regime between a stratified flow and a turn-jet flow. It seems that the principal cause is repetitional generation and disappearance of a circulating flow formed behind the jet due to an interaction between unsteady behavior of a secondary flow in a decay process after the bend and the wakes formed behind the jet, which leads to the vigorous oscillation of the jet near the wall.