Blame attribution (who is to blame for problem causes) and solution attribution (who is to control problem solving) are two critical dimensions of responsibility attribution in psychotherapy. The present study aimed to (1) investigate the impacts of blame attribution and solution attribution on session outcomes from both client and therapist perspectives and (2) clarify the relationship between the therapist-client congruence of responsibility attribution and session outcomes. A total of 69 clients were recruited at a university counselling centre. Client-rated responsibility attribution (to what extent they were responsible for the causes and solution of their current concerns), therapist-rated responsibility attribution (to what extent they thought their clients should be responsible for the causes and solution of clients' current concerns), client-rated session quality and symptom level for each session were collected across 387 sessions. Multilevel regression was used to explore the relationship between responsibility attribution and session outcomes. Truth and bias model and response surface analysis were utilized to analyse the within-client and between-client client-therapist congruence effects. The main results included that (1) the clients with higher solution responsibility had more symptom improvement and higher evaluation of session quality (between-client level). A client's perceived solution responsibility predicted better session quality and fewer next session symptom levels (within-client level). (2) If a therapist attributed more solution responsibility to his/her client, the session quality was higher (within-client level). (3) Neither clients' nor therapists' perspectives on blame attribution directly affected session outcomes. But the higher the client's blame for his/her problem causes, the stronger the association between solution responsibility and symptom reduction (within-client level). (4) Higher within-client client-therapist congruence on blame responsibility led to better session outcomes. The clients' solution responsibility and client-therapist congruence on blame for problem causes contribute to session outcomes in psychotherapy.