Background: A means of assessing the social support needs of spouses of patients with cancer is not available in Japan, yet such individuals are at increased risk of developing psychological difficulties. Objectives: The present study aimed (1) to describe the social support needs of spouses of patients with cancer, and (2) to explore factors associated with social support needs of spouses of patients with cancer. Design: Spouses (n = 559) of patients with cancer were recruited by registered agents of an online survey company and completed a self-reporting, online questionnaire. Measurements: The questionnaires included demographic information and a tool to assess social support needs. Results: Factor analysis of social support needs of the spouses of patients with cancer indicated that (1) “social support needs regarding disease and treatment of patient” (54 items) comprised 3 factors (“medical condition and cure”, “daily life and social support”, “intimacy and employment”), and (2) “social support needs of spouse (19 items)” comprised 2 factors (“family psychological issues and social support” and “intimacy, employment and society”). The ANOVA and T tests showed that “younger age”, “under treatment”, and “cancer not cured: treatment stopped”, “PS1” and “PS 2-4”, the presence of “lung cancer”, and “recurrence/metastasis” were significant factors (all p < 0.05). Conclusions: The age of the spouse, treatment status, performance status, site of cancer, and recurrence/metastasis are important factors related to spousal needs for social support. Clinicians should assess these factors and the social support needs of spouses to provide appropriate support.