The phase behavior of the hydrogen-bonded poly(N-vinylpyrrolidone)-p-dodecylphenoI (PVP-PDP) mixture in toluene solution was investigated. When the concentration of the PVP-PDP mixture in the toluene solution is lower than 10 wt%, the solution formed a clear sol. In the sol situation, a micelle consisting of the PVP core and the PDP shell was formed. Comparison of small-angle X-ray scattering (SAXS) measurements with theoretical scattering profiles calculated for some models indicated that the PVP-PDP micelle took a rodlike form with a 12 nm cross-sectional radius in the sol situation. On the other hand, the toluene solution of the PVP-PDP mixture formed a gel when the concentration of PVP-PDP in the solution is 10 wt% or above. SAXS analysis indicated that the rodlike structure of the PVP-PDP aggregate was maintained in the gel situation.