"Background: The numbers of pets are larger than the number of children in Japan. Dog owners recognize that dog walking stimulates interpersonal relationships between strangers and acquaintances in the urban community. Purpose: To clarify whether dog owner’s personal networks sustain growth quickly and to know what the trigger of making networks is, we monitored and compared the network structures, which were created by “dog walking” and “other” regular activities such as neighbors chatting and community circles. Method: The subject locations were situated in a 2 kilometer radius of an urban residential area in Tokyo. The participant was 68 years old, and she resided in the area. She also used the area for her dog walking. Five surveys were performed at 6 month intervals between 2004 and 2006. A ""P.D.M.(Psychological Distance Map)"" was used to chart her “ego-central” networks. The procedures were: 1) draw a little circle to track acquaintances on the map, indicating psychological distance, 2) draw lines between members who know each other, 3) draw dotted lines to establish groups, 4) the circles on the map are then color coded to depict the strength of relationships. We analyzed and compared the network sizes, network densities, and strength of the relationships. Results: As a result, 1)“Dog Walking” network size expanded four fold from the first survey. 2)The “Dog Walking” network density ratio was ten times lower than the “Other” networks. Both of the network’s densities maintained the same ratios regardless of fluctuating size. 3)The strength of the “Dog Walking” relationships varied. Over half of the original members, who had weak ties in the beginning, built strong relationships over the period of this study. 4)“Dog walking” members were gathering into regular groups. “Other” network members belong to common groups such as “Neighbors” or “Community service members”. Discussion: We confirmed that “Dog Walking” networks expand quickly compared with “Other” networks in the community. The interpersonal relationships between strangers are usually very weak at first, but the relationships become stronger quickly. Gathering points stimulate expansion the network. These results are influenced by environmental conditions such as weather, season, place, time, and facilities. In this case study, we found that the function of “dog walking” promotes healthy aging and is a positive stimulus for the growth of personal networks in the community."