「語彙的習得」常為評價外語能力的一個指標，語彙量多寡不只影響「說」、「寫」的表達能力，對「聽」與「讀」也深具影響。但所謂「習得」的標準多重，因使用目標而不同。本論文從中間語言的立場，探討日文系學生所書寫的作文，調查日語語彙習得之狀況。目的是了解初級至中級的臺灣學習者，所「書寫表達的語言」呈現什麼特徵。作文資料採自四名日文系學生，從一年級第二學期至二年級第一學期的十個月裡，每個月採集一次約600字的作文（未經修改），共十次。探討學生接受日語課程教學一年裡，使用的「語數」「語類」有何變化？ 本論文分析焦點的「語數」包含一篇作文中的總語彙數、個別語彙數、總形態素數、句數、與MLU；「語類」則包括名詞類、動詞類、形容詞類、副詞類、助詞類、接續詞類、連體詞類、連語類等八項。 經研究發現以下特徵：1.語數量的數值變化非直線成長，但後半年呈安定成長狀況。2.一篇作文中的語彙個別數，四人個別差異性大，其數量與成績有相關關係。3.MLU呈緩緩增加狀況，特別是後半年增幅顯著。 關於「語類」則發現以下特徵：1.名詞類的使用量最大，且漢語彙之「正用」比例高，其中包含複雜的複合語彙，超出教材範圍。2.動詞類以具體動作性為主，抽象性概念性較少。3.形容詞整體「個別語彙量」偏少，以屬性、形態描述為主。4.副詞的使用顯現個別差異，擬聲語擬態語則未出現。5.接續詞類只出現5、6詞，反覆使用。 量的成長顯示個別差異性，整體可看到共同使用頻度高的語彙，是屬於習得容易部份，後半年的成長增幅顯著者為暑期赴日研習者，與參加語言能力測驗者。

Vocabulary acquisition is one of the markers for judging the progress of foreign language learning. It affects the four skills of language acquisition. This paper takes interlanguage perspective and studies the vocabulary acquisition of Japanese majors from their writing assignments. The objective is to understand the characteristics of vocabulary acquisition of students from beginning to mid-level. Data collection is taken from four Japanese majors. We focus on the Frequency and number of certain vocabulary and the learning pattern of parts of speech. The samples are from their monthly writing assignment, average 600 words, taken ten times in total during their first year. Our study results in the followings: 1) there is no linear progress of numbers of vocabulary acquisition but our data shows a more steady progress in the second half of the year; 2) individual variations are prominent but there is a correlation between good grades and great numbers of vocabulary; 3) the growth of MLU increases slowly but accelerates during the second half of the year. In terms of their learning pattern of parts of speech, we have found the followings: 1) the numbers of nominal and nouns account for the most; 2) the use of verb is limited to concrete description; 3) adjective usage is limited to categorical references; 4) more idiosyncrasy in adverb usage, no onomatopoeia is found; 5) serial verbs only show up for repetition.