Nylon-66 was melt compounded with 5 wt% nanosized organoclay varying the mixing rate and mixing time and their effects on the structure and properties of the nanocomposites were discussed in terms of the dispersion state of nanoclay. For the preparation of the nanocomposites, the total apparent shear (mixing rate${ imes}$mixing time) was fixed to 450 at three different combinations of mixing rate (30, 60, 90 rpm) and mixing time (5, 7.5, 15 min). While the pristine organoclay showed a (001) peak at $2{ heta}=4.9^{circ}$ in the WAXD patterns, nylon-66/clay nanocomposites gave the disappearance of the peak regardless of mixing conditions, suggesting an exfoliated clay morphology in the nylon 66 matrix. The exfoliation of nanoclay in the nylon-66 matrix was also demonstrated by TEM measurements. On the contrary, rheological measurements revealed that the dispersion state of nanoclay was significantly influenced by the preparation conditions. The dynamic viscosity (${eta}$) of nylon-66/clay nanocomposites was increased as mixing rate was increased. For the normalized viscosity (${eta}{prime}(t)/{eta}{prime}(0)$) obtained by time sweep at a given frequency, all the nanocomposites presented a decreased and upturned trend at the measuring time of ca. 500 s, while nylon-66 showed an increased one over the entire time range. Nylon-66/clay nanocomposites gave lower value of tan${delta}$ with increasing mixing rate. In the logarithmic plot of storage modulus versus loss modulus, the nanocomposites prepared at higher mixing rate gave smaller slope, indicative of an increased heterogeneity. Nanoclay played a role of nucleating agent for nylon-66 by increasing the crystallization temperature, which was more pronounced at lower mixing rate. The induction time rheologically obtained from time sweep measurement at 1 rad/s at $235^{circ}C$ was shorter for the nanocomposites prepared at lower mixing rate, but at 3 rad/s it was little affected by the preparation conditions.