Background and Objectives: There are several tests to determine the type and severity of aphasia, but they take a long time to administer when assessing aphasic patients. In recent years, the analysis of spontaneous speech has gained great attention because it is important to diagnose and follow post-treatment improvement in aphasic patients. This study was done to assess some parameters of connected speech in aphasic patients. In addition, the correlation between connected speech parameters and the type and severity of aphasia was measured. Methods: We compared the connected speech parameters of 27 aphasics (10 fluent and 17 non-fluent), Persian speakers, compared with the control group. There were two groups matched by age, sex, and education. Nest’s bird story pictures were used to elicit a speech sample. In the next step, the connected speech was analyzed to define speech parameters, including speech rate, mean length of utterance, number of utterances, total words, content words, function words, nouns, and verbs. Moreover, the severity of aphasia was measured using a Persian Western Aphasia Battery (WAB). Results: The findings showed significant differences between groups in all parameters of the connected speech (P<0.01). The correlation coefficient between speech parameters and severity of aphasia demonstrated that all parameters were highly correlated (r >0.71) with the severity of aphasia (P<0.01) except for speech rate and the number of function words. There were some typical differences between linguistics grammatical and pragmatical characters of different types of aphasia. Conclusion: Connected speech is one of the most sensitive parts of language in all types of aphasic patients. There are some clinical signs for differential diagnosis of aphasia based on speech measures. According to the findings, the type and severity of aphasia and connected speech were highly correlated. Thus, the use of the connected speech analysis is necessary as an assessment tool for the diagnosis of aphasia.