To determine the face, content, construct validity, and reliability of the functional social support domain of Perinatal Infant Care Social Support (PICSS) translated into Spanish and adapted for first-time mothers of term babies.Validation study of the functional social support domain of PICSS, which has 22 items with response options from 1 to 4; higher scores indicate greater social support. A translation, back-translation, and cultural adaptation process took place along with an expert review to evaluate face and content validity. In total, 210 mothers participated to establish construct validity and the reliability of the domain. The content validity index and factor analysis were used to identify the structure of the domain. Reliability was estimated using Cronbach's alpha coefficient.Linguistic and cultural adaptations were performed, along with validation and reliability. Face validity for mothers was the following: high comprehension (94%); and for experts: high comprehension (95.83%), high clarity (96.53%), and high precision (92.82%). In relevance and pertinence, the content validity index was high (0.97). Construct validation identified two factors that explained 76% of the variance of the domain evaluated: factor 1 "Supporting presence -emotional and appraisal support" (13 items, 39%) and factor 2 "Practical support -informational and instrumental support-" (9 items, 37%). Cronbach's alpha value was 0.97.Given the robust psychometric properties of the Spanish version of the functional social support domain of PICSS, this may be used to identify the functional social support in the mothers.