In this paper, the ten-year (1996–2005) total ion density <I>N<sub>i</sub></I> measurements from the Defense Meteorological Satellite Program (DMSP) spacecraft in the morning and evening (09:30 and 21:30 LT) sectors have been analyzed to explore the dependence of plasma densities in the topside ionosphere at middle and low latitudes on the solar activity level. Results indicate that there is a strong solar activity dependence of DMSP <I>N<sub>i</sub></I> at 848 km altitude, which has latitudinal and seasonal features. The plasma density in the topside ionosphere has an approximately linear dependence on daily F107 and a strongly nonlinear dependence on SEM/SOHO EUV, such that the change rate of <I>N<sub>i</sub></I> becomes greater with increasing solar EUV. This is quite different from the dependence of <I>N<sub>i</sub></I> near the F-Region peak (<I>Nm</I>F2), at which the rate of change of <I>Nm</I>F2 decreases with increasing solar EUV. The rate of change of <I>N<sub>i</sub></I> at the DMSP altitude is greatest in the latitude range where <I>N<sub>i</sub></I> is greatest during high solar activity. We suggest that this greater rate of change (or amplification effect) of <I>N<sub>i</sub></I> at the DMSP altitude is mainly a consequence of the solar activity variations of the topside scale height. The changes in the height of the F-Region peak (<I>hm</I>F<sub>2</sub>) and the density <I>Nm</I>F2 play a secondary role.