This study was to investigate the behavioral specificities of spontaneously hypertensive rats (SHR) and compare them with Wistar-Kyoto (WKY) controls using a 1-year longitudinal study of locomotor activity. Rat locomotor activity was examined every week at 4-12 weeks of age and every month at 4-12 months of age using an Automated Digiscan Activity Monitor system. Six behavioral variables were collected and analyzed: horizontal activity (HA), total distance (TD), movement time (MT), vertical activity (VA), stereotypy count (SC), and margin time (MGT). In general, a significant weekly and monthly age-dependent change (p<0.01) in SHR was shown in the HA, TD, VA, SC and MT variables, whereas MGT showed no significant differences (p>0.05). However, except for the first observations, SHR was significantly hyperactive relative to WKY for HA, VA, TD, MT and SC (p<0.01) before 6 months of age. MGT in SHR were significantly lower than those of WKY (p<0.01) before 3 months of age. Only for VA, SHR was more hyperactive than WKY (p<0.01) and sustained for 12 months in age. From the present results, by extending the observations of locomotor activity testing from 4 weeks to 12 months of life, we were able to observe an interesting strain difference between SHR and WKY in the development pattern of spontaneous activity levels.