New photometric observations and analyses of the W UMa-type binary system RT Leonis Minoris are presented. A period study with our four times of light minimum, including other eclipse times from the literature, suggests that the orbital period of the binary star is variable. The O-C curve can be explained as a cyclic variation with an amplitude of 0.0049d and a period of 46.7yr. Photometric solutions were derived by using the 2003 version of the Wilson-Devinney method (1971, ApJ, 166, 605), and absolute parameters of the system were determined. The results indicate that RT LMi is an ambiguous W UMa-type overcontact system for the following reasons: (i) the depths of both minima are nearly equal, which makes it very difficult to distinguish whether it belongs to an A- or W-type system; (ii) the primary minima in Hoffmann's light curves are an occultation, indicating a W-type system, while the primary minimum in our light curve is a transit, suggesting an A-type light variation; and (iii) though our light curve shows an A-type variation, the photometric solutions indicate a higher secondary temperature of T2= 6513K (T1= 6400K), making the binary system, surprisingly, of W-type. These may indicate that Binnendijk's classification based on the shape of the light curve cannot reveal the physical properties of W UMa-type binary stars of this kind.