Background: Although research showed that positive aspects of the lockdown were perceived during the pandemic, there are no tools to test the positive impact of mandatory social isolation on life. The present study aims to validate a newly developed, brief, four-item perceived positive lockdown impact scale (PPLIS-4). Methods: A cross-sectional online survey study was formed among 4370 adults in three samples: Sample 1 consisted of university students from Poland and Ukraine, Sample 2 consisted of Polish university students under 26 (emerging adults), and Sample 3 consisted of Polish and Ukrainian adults above 25 (non-emerging adults). The standardized questionnaire was used for criterion validity to measure life satisfaction (SWLS), perceived stress (PSS-10), anxiety (GAD-7), and depression (PHQ-9). Results: The exploratory factor analysis (EFA) showed a one-factor solution in Sample 1 in Polish and Ukrainian university students. The confirmatory factor analysis (CFA) and confirmatory composite analysis (CCA) showed the one-factor structure appropriate for the PPLIS-4 among emerging and non-emerging adults. Criterion validity was also confirmed since the PPLIS-4 was positively related to the SWLS and negatively related to stress, anxiety, and depression. Conclusions: The PPLIS-4 is a short but valid questionnaire to assess the positive aspects of lockdown. The PPLIS-4 can be used during the COVID-19 pandemic to measure some positive effects of changes in lifestyle as an aspect of resilience.